Round-up before reseeding?

[W.D.]

My front lawn is 90% crabgrass and I'd like to start a new lawn this Fall
with either a heat resistant fescue or a heartier variety like Bermuda or
St. Aug (I live in Atlanta & get almost full sun). Two questions:

1. should I just use Round-up to kill everything off first or is a
weed-killer a better choice?
2. Can either Bermuda or St. Augustine be started from seed and what are the
pros/cons of these varieties?

Thanks,

W.D.