re part 1)

A mixer will help you in any gig situation. In large venues the engineer should take a feed of your submixer (mixer) and give you a monitor feed back. This means you shouldn't need your own PA. If you're playing venues without a good set-up (ie bigish front of house mixing desk and a GOOD monitor mix on stage you may want to get your own speakers.

But if you have a mixer you'll find that you'll be able to produce (to a reasonable degree) your own tracks at home using any piece of sequencing software. This is very good fun. Very very good fun.

2) You should be able to edit loops via a PC with MESA software by Akai (visit Akai web-site). I have a S3000 and I only ever tried it once out of curiosity. It worked. Then it crashed my mac to hell, but I think it was my own fault.

Good Luck. Post again if you need clarification of anything.

Mike