I would say that listening back to your raw multitrack recordings can be one of the most depressing experiences in the world.
What sounded wonderfully full and natural in the room is now flat, thin, tinny and often quite unmusical. Unless you're lucky, each recording will demand several hours of hard work to knock into shape.
This is not to mention the occasions when not all the instruments are actually put through the soundboard ie most small/bar venues - so you'll need your own mics, stands, leads and possibly pre-amps for those missing instruments.
Plus with only 8 channels, how are you going to share the feeds from the stage out? You can reasonably expect 2 or 3 vocal mics, two guitars, bass, maybe a keyboard plus a minimum of bass drum, snare drum and two overhead mics. Plus you'd really want a mic or two to capture some room ambience. That's easily more than eight...
I love doing multitracks but we run a 24-channel deck, have three crates full of leads, adaptors, preamps, mics and various odds and sods, around a dozen mic stands, a mixing desk, a set of drum mics and a pair of 8-channel isolated mic spiltters. And we still end up struggling with one thing or another...
I would say - start by running a decent pair of mics to record the room. If you have access to the board, complement these with a stereo feed - excellent results can be had with careful mixing of these four channels. And then, if you like what you're doing and are up for the challenge, consider the long, slippery, expensive road to multitrack...