First off, I used the term "fill coats" to describe the adding of resin AFTER the
glass to smooth the surface. Not the resin coat on the raw wood to promote adhesion.

My comment about not using a fill coat meant: that on the interior the surface doesn't need to be glass smooth. And the bagging process will eliminate pinholes. So you probably don't need any smoothing coats after the initial glassing of the interior. If any, just a very thin sealing coat.

I envisioned the process going like this...

Strip the entire kayak. Split the halves.
Glass the exterior of one half (bottom/top doesn't matter to me).
Add resin & sand exterior until surface is smooth. Or maybe stop after one coat, to get the interior done before it warps.
Vac bag layup the interior of the half that is done on the outside.
Do the other half similarly.

My responses on the bagging... again with the disclaimer that I've never built a kayak or bagged over cedar...

unlike a regular layup, I deliberately apply excessive resin when bagging. Not tons of excess, but you NEVER want too little. The bagging process squeezes all the excess up through the peel ply into the absorbent layer. It also leaves practically zero bubbles (they get 'sucked' out). The removal of excess resin, and the removal of resin between the substrate and the cloth or between layers of cloth, and better bonding to the substrate is what I see as the major advantage of bagging. I haven't had good results with bagging forcing epoxy into small irregular interior shapes.

You've GOT to do a test panel to believe it. The cloth and resin get so squashed onto the substrate, it's REALLY cool. And the finished surface looks like the original cloth surface (only clear), because it gets so fully impregnated with resin and has 0 excess. The vacuum will also draw the resin into the substrate pores, so I doubt there would be any adhesion problem, unless it ran dry of resin (again that never use too little issue).

My vacuum setup does have a tank, which acts as a drip catch, but I've never seen any go in the hose, never mind all the way to the tank. Fact is, the tank doesn't help if you have a persistent leak. All it does is make the motor cycle slower. Same percent run time, just longer intervals. I've also never used genuine mastic, I've always contact cemented my 'bags' shut. I use dropcloth poly for bags, fold it over the work, spray around the edges and stick it shut. Nylon "parachute cloth" works for peel ply. And terry cloth towels work for the absorbent layer!