Energia is long gone. RD-170 family is alive and well though. You'd still need a good sized hydrogen engine - a kind of SSME or RD-0120. But may be you just d

Energia is long gone. RD-170 family is alive and well though. You'd still need a good sized hydrogen engine - a kind of SSME or RD-0120. But may be you just don't need too big of a rocket. 25 tons on LEO could be enough for everything, and you'll launch that often enough so a single launch won't be expensive. You can assemble stations, create orbital fuel depots, even make on-orbit manufacturing if you want something really big in one piece.