the iTunes account will let you down load Apps, including the GO4 and UAV forecast apps etc.
I don't do music either.
the unlocked GMS only means that you can suppose buy a cellular plan from any GSM provider. Not sure how that all works, since I have a Verizon Plan. just do a search on "unlocked iPad Air" there is a good article in PCmag.com that takes about it.
As far as updates go, So far "knock on wood" I have not had any problems with the update process or with the FW and Apps updates themselves. But you need to do what you are comfortable with. I read the forums, listen to what people have to say and also what they aren't saying, and make my decision. Some have experience and some don't. Just know, that once you make your decision you are making it with all the best information you have at the time. There is never a right or wrong decision.