Swim rules in pool swims are quite simple
When you enter, you will be asked to put your estimated time down - they will set the slower swimmers off first and each goes about every 10/15 secs (depending on numbers)
Drafting is inevitable but if you do come across a slower swimmer, etiquette says tickle their feet to let them know you're there - they should then stop at the wall and let you pass as you turn. And same goes for those coming from behind on you.
Yes, you can push off but usually tumble turns aren't allowed.
Front crawl is normal; you can use breaststroke; never seen anyone doing fly; backstroke is a no go due to sighting issues. Also, if in difficulty, roll onto your back and hold the lane rope; or stop at the wall end.