1. Somebody else will have to answer this one. I think it's a bad idea- okay for a motorcycle, not so good with all the sensors on this car.
2. Do a search on the forum using "4.10" - prices are all over the map. I plan on doing the 4.10 gears soon. A lot of potential for screw-up here. Find a reputable shop and pay the asking price- it's worth every penny. I would do it myself, but I cannot bring myself to buy the instruments that I will only use once.
3. I have a predator tuner and regret it- If I knew then what I know now, I would have gone SCT. Most serious tuners in here are using SCT and either the mail order tuners you listed, or personal dyno tuners. I guess if you find a guy with a dyno that really knows his caca, you can end up with something better than you can get in the mail, but I'm only going on what I have read in here.
Search the forum- all these questions have been asked and answered before, so most won't waste the time to answer them all over again. I just have a lot of time on my hands today...
Good luck to you.