Ivanhoe, I am relatively new to ARs myself but getting wiser all the time because of this site.
The AR by design is a relatively accurate gun, so most any AR wil be plenty accurate for target shooting and general blasting. So unless you plan on doing serious long range target shooting, you don't need to buy the full length barrel. With that in mind, buy whatever overall length appeals to you.
Alot of people on this board decide on the configuration of their AR simply based on what they want it to look like, especially if its just for blastin.
As stated above, an A2 upper has the carry handle, and the A3 is removable. Not all A3 uppers include the removable carry handle in the price so keep this in mind. Also if you get the A3 without the carry handle then you won't have any rear sight so you'll have to do something about that.
Grips, there are alot of choices for the furniture on an AR. Maybe you could be a little more explicit in what your question is about this. Depending on wether you build a kit or buy a rifle, you may be limited in your choices of furniture.
My best advice would be to ask alot of questions, and read alot of posts here to make sure you understand your options. I think you'll find most people here to be very helpful.