The best advice on what to charge would be to call around town and price the "other guy's". This gives you an idea of what the market is in your area. Remember to compare "apples to apples" though. If you can only supply a "B-rig", you won't be able to charge the "A-rig" rate. I'm here in Baltimore and there is a lot of sound/lighting company's in competition! Average club show from 100-300 ppl avg. charge $300 for B-rig and 16 can lights for local club. Almost all of them can supply sound and lights. And most have multiple rig's and tech's and can take on more work and supply the bigger rooms/events. Don't take on anything you can't handle no matter what you charge! Word of mouth is a good and bad thing in this business.
Equipment damage is going to happen but you should tell the act up front that if they "intentionally" break something they are responsible for replacing it. I lost 3 drivers in my monitors when a singer walked up to each monitor and dumped water into the horns! When I asked this a$$hole why, his reply was "I got caught up in the song dude!" That moment cost the band $300! Drum mikes are going to be hit if not placed correctly. I have been using "less expensive" mic's on drums (Superlux, AKG, A/T) and try to keep them out of the line of fire.
Ken