I mentioned AT4040 or SM57 because they are probably the best all-purpose mics. You can get good results of almost any source with any one of them. Vocals, guitar, bass, acoustic, percussion... hell, even kick drum if you just close mic and then replace the hits with samples via plugin.
I don´t think a treated room is a MUST because I´ve heard far too many great mixes made on regular rooms, but no doubt that they are a very good investment. Anyway, as I said, I believe any good audio engineer can track and mix a great song using only those few things.