Gaining 200 state legislative seats would be a win. Gaining 400 would be a big win.
As for Congress, gaining two House seats for every Senate seat lost would be a win, given the map.
No, that would be objectively terrible on all accounts. This is probably one of the dumbest things I've ever read on this forum. Say Dems lose 10 Senate seats, the ones in Trump states (there's zero chance that happens, but just for the sake of argument). That's still be only 20 House seats. Not worth it at all because the GOP could pass anything they wanted in the Senate and hold the chamber for the next decade for only a small tradeoff of a reduced House majority. A Senate seat is worth about 20x more than a House seat in terms of importance (technically 4.35, but a Senate majority is infinitely more valuable than a House majority.
Yeah but you have to take expectations into account, since the Senate map looks very bad. If you assume a Senate seat is worth 20x more than a House seat (which I don't necessarily disagree with), there's no way Democrats can win in 2018. Might as well pencil in the loss today.
Anyway, that was secondary to my point about state legislative seats.