I assume you mean a dish, not an antenna. Pointing a slimline is not too hard if you follow the directions that come with the dish. Like most jobs, the more you do it, the easier it becomes.
Getting a used receiver is a crapshoot. I would not do it. For a small charge, DirecTV will give you a new one. If it ever goes bad, you can get a replacement for twenty bucks.
Some receivers need the B-band, some do not (it may be built in, depends on the receiver model). Again, if the receriver you get from them needs one, it will be included. If you need one and it was not there or goes bad, they will send you a new one for free.