I work in that order pretty much. All the cutting of slots and drilling is done before any covering goes down, but before I glue the hinges in I will cover just the areas that become unreachable when the control surface is installed. Here's a good example of this technique on a build I did a while ago:
View attachment 198997
The wingtips and center section are also covered, but that's of no concern. You just cover the interior of the cutout for the aileron and just a little bit of the top and bottom surface directly next to it. You only need to go outwards maybe 1/8 inch, and this leaves the hole for the toothpick uncovered, so the toothpick can be glued in and sanded away without sanding scratches into the covering. At this stage also cut out the main wing covering to shape using the aileron cutout and wing themselves itself to trace it, but don't apply it until the aileron is installed. Make sure not to have any covering that oversteps into the aileron cutout as trying to stick it down is a pain and it also looks ugly going around the corner unless you cut it - and plus, you have a bit of wiggle room provided by the covering applied before the aileron went on. It's less critical to get a healthy overlap here because this is an electric airplane, but on nitro planes you
absolutely must seal this as well as you can or else oil will creep in and ruin the wood.
It's worth noting that I prefer to glue the hinges into the control surfaces first. I don't know why, maybe it's just a me thing, but I always have much less trouble trying to slot in hinges glued on the surface side first.
Another tip very useful with the lighter colored films is that to avoid losing your slots under the covering, go over them with a sharpie. It will show through the covering and then when you go to cut a slot through it you don't have to hunt down the slot in the wood all over again.
Four on each aileron, five on the elevator, and three on the rudder. That's what I would do if I was the one building this plane. It gives redundancy if you break a hinge while not being overkill. (Hinges have weight too, it's small, but assuming objects to be massless does not help build light airplanes)
Funnily enough a long time ago I figured out this really complicated formula for that exact task, taking into account things like the intended airspeed, wing loadings, intended hinges, bending strength of the control surfaces, all that jazz... but just eyeballing it works good enough, so I don't even use it anymore
Hinge placement matters a lot too. If you can, put a hinge directly in-line with wherever the control horns on each surface are. A lot of the time people don't do this, and it costs control authority because the force applied to the surface by the control horn will often go towards bowing the surface up and down a small amount between hinges instead of actually moving it, which placing a hinge right there will eradicate. It also helps reduce twisting forces applied to the hinges which will help them last longer. It also allows you to skip pinning that particular hinge as often the screws holding the control horn on will take over that job instead.
