1. no - they will not be affected until you distribute your new rev of the front end to them. you can have multiple different font-ends (e.g. different releases of your front-end) looking at the same back-end data at the same time.
2. pass - depends on your security setup. almost certainly you will have some permissions juggling to do.
3. no - best to keep the front-end on the client and the back-end on the server. (reasons: performance, net-traffic, and what else are you going to do with the client disk space anyway?).