Yep, Jon. Just the painted map. Baking is sorta cheezy IMO.
Loc... It'll begin to dog when the layer count gets up there. That's normal. There used to be an actual 100 layer limit set by PS up until maybe PS7.
Be real careful with this actually... Ya know how the scratch disk file size blows up when you open a 20MB or so sized .PSD? Well, I actually created a file that once closed couldn't be reopened on the same machine because there wasn't enough RAM. I actually use several PSDs sometimes for different phases. For example, I have a seperate PSD for the M16 series that's for swapping handguards, iron sights and dirtmapping.
What I generally do is texture each part/mapping segment of the model with it's own group of layers (slide, barrel, magazine, frame, etc) and then make a merged copy of group (ctrl+alt+E) once I'm ready to move on and hide the regular layers so it isn't so taxing. It greatly speeds up performance. If I need to go back and tweak something, I just delete the merged layer and work inside the group.
My rig is showing its age but it was set up for this kind of thing. 2GB of fast (for its day) RAM and a small but high RPM disc for my C drive to cache on. 1000:1 contrast on my monitor. I use CCleaner several times per session too.
Filya... I use [self-edit] loads of layers mostly because I can

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Layers, layer groups and quickmask make my photoshop world go round. If everything's layered up nicely I can easily "tetris" the contents to make the most of my pixels or make adjustments to complex shadows or highlights by clicking layers on/off. Some PSDs turn out to be much more complex than others and I guess it really comes down to how much I want to leave a back door open for myself.... In the case of these guns, I want to leave that door wide open to facilitate color changes and multi-engine, multi-shader usability.
With metal objects, sometimes I just find that to build a really smooth highlight or shadow, it takes several layers with duplicate image content but different layer settings all piled on top of each other to get the effect that I want.
Wow, sorry for the longwindedness of this. I could actually go on-and on but I won't. The short answer is that I'm just an uptight pixel-pusher. In stark contrast, however, I collapse the stack in max after almost every modifier (shrug).
edit: omg three posts since I started this reply LOL. I must be sleepy.