Hi,
Being a longtime modeler of just about everything, I find myself making up subassemblies that go inside then once the major unit, Plane, Tank, Ship, Weapons System, Whatever, is finally together, in goes all the stuffing I can add without breaking anything and then it get sealed up so that none of my carefully assembled, washed, drybrushed and sealed with flat or gloss, depending on the subject, subassemblies gets overspray on it. Once i am satisified that I can paint away without affecting anything I've added inside I get happy with finishing the exterior and hammering the outside paint on. Once I am satisfied with that i get all the washes and dry brushing done and when it's all done I unmask and do final cleanup and assembly. I got in the habit of doing it this way after a while working as a paint and body tech in body shops and car dealerships. It's pretty well how they do it there and it usually comes out great.
Of course that's just the way I do it, in modeling, to each his own and if it works for you, great. It's awful hard to make painted things stick to each other with any kind of glue, the plastic cement just gives it up after a while, the cyroanalates will hang onto the paint really well, so well in fact that it often just peels the paint right off the subject leaving you with 2 pieces, one of them with a little less paint on it than the other. Life is just not fair.
I've thrown my 1.4 (2 cents adjusted for inflation)cents in and now I'm gonna crawl back out here in cyberspace and contemplate the vagaries of the SdKfz 251troop transport I'm working on for the DSB contest. Good luck.