1) How difficult is it to rewire this AEG to use the Crane style stocks?
As the others have said, likely the better route is to get a CQB and replace its 10.5" barrel with a 14.5" barrel to achieve that M4 look. This is probably a more costly approach, but the end result will be considerably greater.
2) How can you adjust the velocity of these guns? Do you just have to change out the spring? Can this be done easily at the game site? Ufortunately the velocity limits vary from game to game it seems so I need to be able to adjust this easily.
Typically spring adjustment is not something that can be done on the fly. While velocity limits do vary, you'll find that once you start playing, this isn't the problem you make it to be right now.
3) How difficult is it to change out the stock barrel for a precision barrel?
With CA guns, this is just about the easiest possible upgrade there is. When you get to that point, there is a lot of info on this forum about such things.
Please keep in mind I have never owned an AEG before. Are there places in the valley that can do upgrades, or teach me how to do them. Any info would be greatly appreciated. Thanks.
There is a ton of information about upgrading guns on this forum and a lot of people who know how to do it.