I have had one since early February, and I love it. As with all other gear, give it a go, and see if it's for you. But I'll give my opinions as to your points....
1. You can use 6 AA batteries. They apparantly last 10-11 hours of continuous use. Or you can use a 9 volt pp3 type, which will last about 1-2 hours. I find the adapter is fine. It is part of the footswitch. It will be a pain if you have wireless stuff for gigs, but I've gigged it no problems.
2. You can, but they sound pants IMO. They sound great through a PA or an acoustic amp. I think that two of the acoustics are really good, one is OK and the 12 string acoustics are ropey. But I don't think you'll find many real electro acoustics that sound there best through an electric amp so we can't hold that against it
3. The 'Mystery port' (TM). Several theories abound, including rumors of future upgrades, simultaneous patch change with other line 6 gear etc. But no-one official seems willing to confirm what it will ever do. If anything.
4. Depends on the model. There is a 12 position rotary switch. Two of these positions are custom banks. The 10 factory banks work in conjunction with a 5 position strat style switch. When you select the strat model, the 5 position switch does exactly what a strat switch does. In the tele bank, there are 3 different teles represented in the 5 available slots. This means no one tele is fully modelled; two positions of two guitars, one of another (does this make sense?). The acoustic bank has 5 different guitars on the 5 positions. Etc. Download the manual from the website for more details.
HTH. Any other questions, give me a shout.