Multiple coats is a great way of stacking tolerances. Just say "no" to that nonsense.
Dry tumble. No BBs. No song and dance. With or without a vibe tumbler, if your powder is good, and you have no moisture or other contamination issues.
Don't waste a single second standing up bullets. That just wastes time and worsens the surface finish on the base of the bullet, which is the most critical area, as it passes the crown.
1) Check your oven's temp against a thermometer. Preheat while you tumble. Follow the directions for the powder you are using.
2) tumble until the coating is thin and uniform on the bullets. If you are having issues, dry them at very low temp, and try again. Or in a vibe tumbler, tumble until they coat well, which is another way of just letting them dry until static builds.
3) Sift off excess powder, and pour the bullets onto a clean mesh rack tray. don't touch them. I keep a clean paint stirrer to spread them out so I don't contaminate them, and I minimise handling. I don't worry about bullets touching, but you don't want large flats in contact. If a couple happen, NBD. Just recast those. It's a better use of your time than fiddling about micromanaging your bullets and messing up their finish.
4) Pull them out of the oven HOT, even a little bit before the stated full cure time. Knock them into a very clean cardboard box, and bash them around. This will let the coating cool, but not allow any to stick to each other. Since the thermo set plastic coating is still hot enough to flow a little, surface tension will even out any minor marks from contact with other bullets or the rack. These will be far less of an issue than the crust ring on the base that comes from over working things and standing them all up.
5) serve with a toothpick, and tell your guests to guess what the flavor is.
6) if you want to size them, do it at this point. Sizing can work soften lead, so you may wish to put them all in the oven after sizing, at 400*f for 40 minutes and then throw the whole batch in water. This will uniform out your heat treat from bullet to bullet and you will be at full max hardness for your alloy. Much less variance than you get from water dropping out of the mold.
I know you've probably read a thousand different strong opinions about this, but that's my .02.
Do no action that lacks a measurable advantage. That cuts out BBs, standing up, naming each bullet and whispering encouragement to it, wearing your lucky socks both on your left foot, silicone mats, and possibly gas checks, though the data conflicts on that last point.
Double coatings are in this category too, since not only are they not providing a measurable advantage, they are necessarily increasing the variability round to round. If you think of the bullet as one component, the first layer as another component, and then the second layer as an other component, it is pretty obvious that each of those has a range of variability to it, and when those tolerances coincide in one spot, they add to eachother giving you maximal inconsistency. Fewer parts is fewer stacked tolerances.