Brick & Mortar noob question

Posting here b/c I don't want to get completely flamed in the B&M forum.

I've only played online, but when playing at a limit table in a casino is there a recommended amount that you sit with? Am thinking that maybe there's a multiplier rule of thumb to use, like 25 or 30 times the big bet, at least for the low limits.

Thinking about playing at a 3-6 table, and was going to take $125 or $150. Is this an ok amount?