multi-branch j-box for residential
I'm installing a new breaker sub-panel that is flush-mount on the inside of a finished garage wall. The back and sides could be accessible from the utility room behind (standard 2x4 wall). Per my local code office, I'll need to have the stud bay behind the panel and adjacent framing to the sides, above, and below, drywalled to meet fire code.
I'd like to run a series of conduits from the knock-outs on the panel to either one large or a series of smaller j-boxes that are accessible in the utility room. This will allow me to fish romex lines into the panel as I migrate them from the original main panel and have a proper junction point if the NM lines aren't long enough or if I want to transition to individual conductors inside the conduits and panel to save space.
Alternatively, for branch lines that don't require a junction, I can simply bore out alignment holes for the conduits in the framing and run the NM lines straight in (with abrasion protection) or cap the conduit if unsued. Are there restrictions on conductors for multiple branches running in the same conduit (other than the obligatory GFCI hot-tub/pool stuff)?
Does this all seem reasonable and have others done/seen anything similar? I may be over-thinking the problem, but I want to leave the panel flush mounted in the garage and reasonably "future-proof" for circuit upgrades/changes without having to re-do the drywall every time.