All great things to consider, thanks all. First off, no worries about the lease ending suddenly unless I really upset the BO. The horse was originally for sale and she agreed to lease him, and I said if you ever get to the point that you must sell him, let me know and I'll make a decision. She really has no advantage to selling him because I'm paying full board/all expenses right now AND she has ownership of the horse. Selling would change nothing except she'd get a lump sum and no longer have ownership. I guess for ME the advantage to buying is that my training would be an investment and the horse would be worth more after. However, I really doubt I would get my training $ back on a resale.
He is just such a nice all-around horse. Very kind, smart, not too lazy and not too energetic, etc. I really like him. I feel like he can do it all--he's done some trails, he's done some rodeo, we are currently riding hunt seat and he's fine, etc. He is a jack of all trades but a master of none. I think training would go pretty fast for him as he's already really good with leads, leg yielding, etc. I like the idea of a horse that can do a lot of things, as my son is only 11 and who knows what his future will be. Right now, he enjoys jumping, but he also enjoys just riding around the pasture and I think he'll also enjoy fun shows/county fairs/etc.
I posted about him once here if you want to see pics: Casper
Another option: a cute hunter/jumper is for sale at our lesson barn. The drawbacks of this horse is we'd have to give up our current two horses to afford the board on this one, as there is no room at our current barn and board is a lot more at our lesson barn. Also, this horse is more of a hunter/jumper specifically and not trained to do anything else (not that he can't learn). He's a really nice horse though. So incredibly gentle. Yesterday the two instructors were goofing around and one threw a plastic mounting block at the other, and Gatsby just stood there. So, I think he'd be a good beginner H/J and our trainer said he has loads of jumping talent. But, I hate to lock in to a H/J when, like I said, who knows what the future will be. Plus, our lesson barn is a QH barn and they do the QH shows...if my son wants to be on their show team, this horse could not do it. If I am going to spend the $ on a horse at this barn, I feel like I should probably go the QH route. Anyhow, if you're still reading
here's a video of the TB: Gatsby
Thanks again for all of the tips. I will mull all of this over.