Trying to start playing again but I am totally confused by new combat system... Catacombs used to be a group/party thing but now it seems like the only way to level? Do I just use the auto pilot feature when doing solo catacombs or whats the most efficient way to level?

You can press t to whistle

WSAD move around or arrows, G to engage (drive around after you kill wave). Or press T to just have normal monsters spawn one after another (as pointed out)

You will only find Maps if you explore catacombs.

And trap doors!
And eps!
And drops!

For fastest climbing you will want to whistle with "T"

For best results MFing you will want to explore manually using the "WASD" keys + "G" looking for EPs and TDs

Note that changing the engage key from G to F makes driving easier

Group climbs are obviously still the most efficient overall