Also check the NASGA site for groups that might train near you. That's where I found the group I train with and my husband and I adore them. They're GREAT help, and they have a lot of the gear already so we can take our time getting things together for our own stuff My husband might even do some weight training with them (I was invited, but these guys are BIG and besides, I thought they might want to cut loose and be guys... not that they hold back around me, but you probably know what I mean).

A doctor would know best if you're able to do anything like this (you mentioned your knees, etc). Technique and form will also help prevent injuries, as well as help your throws. It's not always about muscle.

I definitely recommend finding some folks you can train with. It's more fun, and it's a ton of help.