If it helps, you may want to research pate de verre. It is fine glass frit mixed with a binder (usually gum arabic) and made into a sort of paste, which is then pushed into a mold (usually plaster and silica). It may be a more forgiving way to incorporate glass, but it is a technique to master in itself. (I haven't done it myself, so I can't give any personal experience here.)
I would recommend picking a specific kind of glass and sticking to it. Using glass meant for stained glass will lead to frustration, as each piece has a different COE and is thus incompatible with other kinds of stained glass. Plus you'll have to develop a kiln schedule for each individual piece of glass. I would recommend using one of the more expensive but more reliable brands meant for kilnwork- Spectrum has a COE of 96, and Bullseye has a COE of 90. There can still be slight incompatibilities but not nearly as bad as you get with "found" glass. One other thing to keep in mind, though, is that glass from recycled bottles has a higher melting point than these glasses do and thus might be better suited for ceramic work. It's tough to find a good kiln schedule for it, though.
Here are some basic starter schedules for each kind of glass. You'll notice that the temperatures and time are very specific. That keeps the glass from getting thermal shock and cracking. There are 2 very important parts to how glass responds to heat: how hot it is, and how long it is held.
Remember that you'll need at least a tack fuse to get the glass to stick to anything- at a slumping temperature it is not molten enough to bind to other glass or materials. Glass slumps before it fuses, so keep that in mind! Don't expect perfectly cut squares to stay put and keep their shape on a curved surface, for example.
Hope that all made sense and is helpful!