You can't leave surrounds behind for an HT, without those, movie watching would not be very exciting. You can actually skip purchasing a sub and a center channel (use a phantom center, as I have read here). Just get M60s and QS4s or 8s now, and save up for a sub and center for later.

Living in an apartment is really an issue for having a sub. This is the main reason I don't have a real ht for now (only a HTIB from three years ago).

Axiom M60s, QS4s, VP100 Onkyo TX-SR804 Oppo 970HD Rotel RB-1080/RCD-1072 REL Q150E sub, PS 3