There is no reason to "dilute paint as you should". You dilute paint if it makes it apply better in the conditions you happen to be painting in. The manufacturer went to great lengths to try to formulate a paint that goes on well, straight out of the can if possible. By automatically diluting it, you are assuming that you know more about paint than the folks who developed and manufactured it, which is very seldom the case. Diluting it with paint thinner lowers the paint's viscosity (makes it thinner or more watery) and in some conditions, allows you to spread it more evenly or keep a wet edge better. This can certainly be helpful at times, but it also makes it more prone to runs and drips. By far, the best advice is usually to follow the directions on the can, where they will usually mention the options for thinning the paint and exactly what product to use to do so, if needed. You do sometimes run into a situation where they are selling you a rather overpriced solvent mixture as their "special thinner" for a particular paint, but considering the labor involved in doing a good paint job, it's usually worth it to stick with the factory-suggested thinner unless you have first-hand knowledge that something else works just as well. If the paint is going on evenly and allowing you to get the desired results straight out of the can, do it - and save the thinner for days when the brush seems to be dragging and you think a bit more flow would help.
There is generally nothing magical about most one-part primers. They don't usually stick any better than the paint itself. Their function is mainly to give you an additional sandable layer between the surface and the final paint finish, so that you have a final chance to get a very smooth surface to paint over. In cases where the color of the surface may not be uniform due to the fairing process, they may also give you a nice uniformly-colored base for your final coats. With some shades of enamel, you might be able to see color variations under the paint and primer may be a good way to prevent that in those situations. So whether it's to help even out the surface texture or to even out the base color, primer can be your pal. Whether or not you need it on a particular job depends on how well you were able to prepare the surface.
For wood/canvas boats, I like the idea of adding just a little bit of the paint to the primer, just to color it slightly. If, for example, the dried canvas filler is light grey, the paint is dark green and the primer between them has been tinted to a light green, then if I hit something and scratch the bottom, it's pretty easy to tell how deep the scratch is and decide what to repair it with.
If you use Brightside enamel over primer, it's probably smartest to also use Brightside Primer. It's a microballoon-based mix that puts down a fairly thick layer of sandable stuff on the surface. Unless you are awfully good at applying it, you can count on being there for a while sanding it smooth after it dries and before painting, because it's gonna' need it. It does offer excellent hiding characteristics for small surface flaws, but the process adds another, fairly substantial, round of work to the project. If I'm using Brightside and can get my surface smooth enough to paint without priming, I'll generally skip the primer. The paint job itself will still stick just as well and last just as long.
As for the paint itself, Brightside is excellent stuff, and unless you're really good with a brush, or have spraying equipment and know how to use it, rolling and tipping is the way to go. The reason that paint drips and runs is because it is applied unevenly and is too thick in some places. The more diluted the paint is, the more prone it is to running. The thicker it is, the harder it is to get it applied in a thin, even layer - so what you are looking for, and what the paint manufactirer is trying to supply you with, is some sort of happy medium that can be used straight out of the can, or if needed, diluted slightly to meet the weather conditions.
Rolling on the paint (or varnish) with a thin, fine roller and rather vigorous strokes is the best way to lay down a thin, even coat that won't drip. The best rollers that I know of for this are the Gougeon Brothers yellow foam rollers made for epoxy work (West Marine sells them - not cheap, but they work great). The drawback with rollers is that in the process of rolling the paint out to a thin, even layer, the roller introduces a lot of tiny air bubbles to the surface. Left alone, many of these bubbles would dry that way. To fix this, we "tip" the paint immediately after rolling. This just means that we take a soft paint brush (some folks use foam brushes, I generally like bristle brushes better, but use whatever you like best) and we drag the tip of the brush over the freshly-rolled paint, using just as little pressure as we can possibly manage. You are not trying to move paint around at all. All you are trying to do is knock down the bubbles. Since you are not moving the paint, you can tip in any direction you want. I generally roll up and down and tip up and down. Some folks do either or both in other directions. If you roll the paint out well enough and tip lightly enough, it should make no difference to the quality of the final finish.
Timing is critical. Thin, rolled-on paint starts to dry quickly and the time window for tipping out the bubbles before the paint surface starts to get sticky is quite short. For this reason, you need to roll a small area (like maybe 24"x24" or less on a canoe), tip it quickly and move to the next area before the edges of the painted area get tacky. Obviously, some prior planning as to where you plan to start and how you will proceed to cover the entire hull is a good idea. Two people, with one rolling and a second following right behind and tipping is the best way to go. When I roll and tip by myself, I have a roller in one hand and a brush in the other, which looks pretty funny, but works with practice. No, I don't do the two steps simultaneously, but it eliminates some time when switching back and forth.
Thin and even without leaving bubbles is the name of the game. If you apply the paint thin enough, the first coat of Brightside usually looks like crap and leaves you wondering whether the whole procedure is a big mistake. Fear not - it's supposed to look like that. If it looks even and glossy, you probably put on too much and are risking drips. Between coats, I usually go over the dried paint with a Scotchbrite pad and it seldom needs more abrasive measures (like sandpaper).
The second coat, rolled and tipped, will suddenly start to look awfully good. Whether or not it needs a third coat depends on the conditions and how thick or thin you applied the paint. In any case, three rolled and tipped coats is usually thinner than two brushed coats, so you don't need to worry about glopping up the surface with extra, unneeded paint. A quart of Brightside (or most enamels) will yield 2-3 coats on a typical canoe. If I have any complaint about Brightside, it would be that it sometimes strikes me as maybe being a bit too glossy on a wooden canoe (looking a bit too much like fiberglass gelcoat) but that depends on what the builder likes. Other than that, it's excellent paint and can generate a stunning paint job.
The sailboat below is Brightside (two coats, unthinned, no primer, rolled and tipped without help out in my driveway). I used dark green and mixed in a little black to darken it. When this photo was taken, the paint job was three years old. The boat had been outside, uncovered all that time and was being cleaned up after a season on the water, hooked to a mooring buoy. We used 3M "One-Step" cleaner/wax for cleanup on the paint. It's a boat wax with just a bit of polishing compound in it and another excellent product. The red bottom paint is made for constant immersion, topside enamel is not, thus the color switch down low. The canoe is also rolled and tipped, but using Ace Hardware porch and floor enamel, specifically because it has somewhat less gloss and doesn't go on quite as smoothly and gel-coat-like as Brightside (pretty cheap, too and lots of colors available).
