Auto gain usually doesn't work well for music, particularly very dynamic music.
That being said, which Tascam? What type of rooms/crowds? Probably, you will want a good pair of cardioid small-diaphragm condenser mics; if money is truly no object, I would look at Schoeps MK4s or DPA 4011s as excellent starting points. If your recorder can provide phantom power to the mics, you may be good to go just mics > recorder. If not, you will need a power source for the mics (either a power only box, like a Denecke PS-2, or a small pre-amp, such as an Aerco MP-2 or Sound Devices MixPre-D). There are a lot of options. Plus, you will need cables, clips, a bar, a stand, etc.
I would also point out that, unless someone at the board can keep an eye on your gear or you can set-up in a protected area, you might not want to leave a (potentially) valuable recording rig to the vicissitudes of the crowd...