No m/am reactor
no universal translator
I would definately have shields. This is one tech that is really a must. Without shields, realistically ship to ship combat would last 10 seconds.
I think it would be a nice change if the UESPA was using Air Force ranks rather than naval just for a change. Colonel Archer if you will. No spatial torpedoes, but fusion warheads instead. I think a mix of lasers or some new kind of particle beam. Maybe away teams could actually use kinetic weapons. Keeping the tech 'low tech' I think really opens aup a new style of story telling. Oh and no subspace communication, our crew is out there and they have to make the tough calls on their own.
As for interstellar relations I dont like Vulcans as the mentor race. It always seemed that Earth was the "real" founder of the Federation. Even centuries later we only see a small minority of starfleet being aliens. No alien crew members, this is an Earth ship. No klingons, theyve been done to death and were 23rd/24th century adversaries.
Mostly I'd have my crew exp[lore strange new worlds. Thats all trek really needs, but it would be fun to have a few of visits to non-warp planets being that theres no prime directive. Maybe explore some real sci fi concepts for a change.