Wow, lots of questions here. I'm not a pro but will only give you suggestions to questions that I feel I can.
1) Not the best idea. You will suffer from a severe restriction in flow rate and thus pressure if you try to run heads off a hose bib. More importantly, you will need backflow prevention on both of those connections. You will spend more in BF protection devices for two water sources, than piping if you have one single source of water.
I forget what the terminology is for the thread on a garden hose. It is different than the thread on NPT pipe. You would need to adapt it. They do make them though.
2) Yes, poly pipe is probably the easiest for a beginner to use and manage. Drain valves are largley not recommended since they wind up eventually clogging and must be installed at the lowest point in the zone with a bed of crushed stone so they can drain.
4) No. But it's probably a lot easier. There is a company "Dawn" that makes a 3/4" poly to funny pipe tee fitting. I think they also make a 1" to funny pipe tee. These are what I used.
http://www.sprinklerwarehouse.com/Dawn-Industries-Irrigation-Insert-Tee-p/1401-099.htm They made life much easier and reduced the number of connections.
5) I don't know the exact answer to this one but I used a 3/4" barb to 3/4" FMT and then connected a 3/4" MPT to funny pipe barb to that for the ends of my lateral lines. At the time, I couldn't find a 3/4" barb to funny pipe fitting.
6) I wouldn't. I installed a drain port at the lowest point in my system. In my case this point was just after the shut off valve for the sprinkler system supply line in my basement. This allows me to open the bleeder on the inlet side of my PVB and drain the pipe down. On the outlet side of the PVB I can connect an air compressor to the bleeder and blow out the lines. You will always have some moisture inside the pipes but you don't want standing water. Standing water can freeze and easily break the pipe. If you don' want burst pipes you will need to blow it out.
7) I'm in NJ and I tried to stay at least 10"-12" below the surface. I would definitely recommend going deeper than 6". If not to help protect against freezing but to avoid you or someone else hitting the lines later on when putting up a tent, sticking an oscillating sprinkler in the ground or digging.