I was taught years ago to use Ronsonol lighter fluid and it's all I've ever used to thin Softex. But anymore, I don't even buy Softex, I just thin Goop adhesive down with Ronsonol. It's way cheaper than Softex, and I don't feel so bad when it dries up because I forgot to thin it.
As far as UV glues, I use mostly Loon UV Knot Sense or UV Aquaseal. Al's Sports has had UV Aquaseal blem tubes on sale for $1.99 for months:
The UV Aquaseal yellows when cured, but if that doesn't bother you it's pretty sturdy. You'll have to coat both with something, I typically use Hard as Hull. I got a UV Light off of eBay for $7.99, works as good as the $60 CCG lights, I've done a side-by-side. This is the one I got:
Hope some of this is helpful!