paytoncool7 there are many many things you can use for targets. I like things like dog chew toys that are tennis ball size and stuffed. They stand up well to being shot time after time.
As far as attachments go - just my opinion here but the fewer the better on the blowgun itself. In fact I don't like any on the BG itself. I carry my darts either around my neck with a magnetic necklace or in a quiver. Those two serve me well in the field. For practice I just hold them by sticking them into a 1 square foot chunk of styrofoam and then grab them one by one as I shoot with the darts in the styrofoam right beside me on a shelf/desk/box what ever happens to be handy at that time.
As most seasoned shooters will tell you, the quivers that come with BG's are pretty useless especially for follow up shots. They hold darts fairly well by keeping a tight hold on them......not what you want for a quick follow up shot for hunting small game or even target practice and having to fight with the little buggers to get them out of the quiver. It's a PITA.
If you keep your BG itself clean and clear of marketing gadgetry there won't be all that crap hanging off your barrel and getting caught or snagged on branches or vines etc. as you walk through the woods. Also, you will stab yourself far less. Plus I myself don't like the way they interfere with my sight picture while aiming. Keeping it simple means fewer things to go wrong when you need things to go right!
Almost anything can be a target. I have shot at soda cans, 6oz steel cans, 3.5" floppy disks. I've heard of people shooting at just the rubber tip of nerf darts. Heck, just make it fun and challenging.
There are many modifications you can do to a BG. I attached a laser sight on one of mine. You can make your own sights. I have used the rear vent of blow dryers. They are perfect. Round, light plastic, and make a perfect sight. I use cork stoppers for dart quivers attached to the BG. Options are endless.