I am not an authority by any means. From what I understand, stained glass is the type of glass used to fuse glass in a kiln. The only warning I've heard from the fused glass studio where I took classes is that, when you are fusing two different pieces of stained glass together, they should be the same COE. So if you are planning to fire your glass in a kiln, you wouldn't try to fuse a piece of Bullseye (90 COE) to a piece of Spectrum (96 COE). It's called "compatibility." COE means Coefficient of Expansion. So, short answer, it should be okay to put your glass in a kiln. You might want to do some more research; try "warm glass" in Google search.

Regular stained glass is not designed or tested for fusing. The colors may not be stable at fusing temps and it can be prone to devitrification.

Silvamae touched on the COE issue. The problem is you have no idea what the COE for non fusible stained glass is, so you should only fuse glass together from the very same sheet.

I have never used a microwave kiln, but I don't think the glass you use will have any effect on your microwave. Make sure you carefully follow the instructions that came with it.