This is exactly what I've been thinking dictates the sequence. To get that sharp line where the side panel veneer meets the front baffle the veneer needs to be done before glue up. I believe my sequence will be:
1. Veneer side panels and mask them with contact paper
2. Glue up (except for bases)
3. Mask front baffle and spray inside flat black
4. Mask inside and spray front baffle and bases with 2 part automotive. This is the hardest to mask due to the round-overs on the driver holes. There is a little margin for error where the driver flanges mate up to the front baffle. I envision using the thin plastic masking designed to cover windows in house painting to envelope the entire cabinet just leaving the front baffle exposed.
5. Remove contact paper and finish the veneer
6. Glue on bases
7. Viola! Ha!
I would install the braces during the glueup. This will insure everything stays in proper alignment and the braces make proper contact on all three sides. If you glue up without the braces, you run the rist of ahving the alignment slightly off and then the braces won't fit properly. You can end up with a brace being slightly cockeyed and not flush with the rear edges of the wings. This is the order I use:
1) Dry fit and clamp everything together, mark a line on both sides of the braces where they meet the wings, and mark a line on the wings where they meet the baffle.
2) Disassemble the cabinets
3) Sand the front edge of the wings to where they are the thickness of the veneer minus the thickness of the paint below the edge of the baffle (you're shooting for having the paint and veneer close to even with each other) this doesn't need to be exact just close, feather this back at least 3" from the edge.
3) Veneer the outside of the wings. I don't veneer the outside (top,back) edges of the veneer. I paint those the same color as the baffle but that's a personal choice.
4) Tape off all edges of the veneer that are going to be next to paint or a glue joint. You don't want any paint or glue to get on the veneer as it will negatively affect the finish
5) Tape off the areas on the outside of the lines that are on the inside pieces (where they will be inserted into the dados or rabbets)
6) Paint the inside pieces
7) Remove the tape from the inside pieces
8 ) Glue up the cabinets. Do not permanently attach the base at this time. You will need to remove do do step 9). Paint the base separately then permanently attach it to the cabinet last.
9) Cut a shallow reveal along the edges of the baffle where they meet the veneer. This will get painted the same color as the baffle and is why you didn't need to get the mating edges perfect in step 3.
10) Tape off all exposed areas that are not to be painted the baffle color
11) Paint the baffle and everything else that gets the same color
12) If the baffle and veneer are going to get the same clearcoat, remove the tape from the veneer and apply the clearcoat. If the clearcoat is going to be different, apply the clearcoat to the baffle color areas. Then remove the tape from the veneer, tape off the baffle color areas, then apply the clearcoat to the veneer.
13) Remove any remaining masking tape on the outside
14) Do any desired cutting, buffing, and polishing.
15) Remove the rest of the masking tape.
16) Touch up the inside paint if needed
17) Attach the base
Now Viola! I use a few more steps....