How do I avoid a melted, droopy, rough surface?

That look means too much heat for your feedrate — the wire is melting a slot wider than itself and the edges sag and re-fuse. The fix is almost always to lower the wire temperature and/or speed up the feed so the wire passes through cleanly and moves on before the foam re-melts.

Also check tension: a slack wire dwells and over-melts. Aim for the wire to glide with a crisp, narrow kerf and a faint glow, not a bright orange. Make small changes, one variable at a time, and cut test slots. A clean hot-wire edge is smooth and slightly glazed; rough, fuzzy, or droopy edges are the classic over-heat or over-slow signature.