I was also going to mention the Romulan Quantum Singularity drives as an alternative to the matter/antimatter reactors used by the Federation. We never really get to hear what other races use for their energy sources, but I wouldn't rule out anything, even ZPE.
As far as needing a compact reactor, even shuttles as small as the Type 6 had a warp drive. The much larger Runabouts and the Delta Flyer also had advanced warp drives. I'm not sure what the absolute smallest warp-capable ship would be, but the tech is certainly there.
I'm not sure of the rationale behind not having fighters in Trek, because from a tactical standpoint it would seem to be the superior method of interstellar battle (multiple attack vectors, minimized casualties, etc). If I had to guess, either Roddenberry or the other producers were trying to distance Trek from Star Wars, where battles were primarily carried out by compact fighters.
I personally would love to see Federation fighters, even if they weren't solo craft and required additional pilots/nav/tactical crew. Fighters was one of the things that made Battlestar Galactica exciting.
As far as what time period, its only a guess but I would say the technology already exists in the current cinematic time period, so we're talking late 23rd century (what year are we up to now in the prime universe, 2390-91?)