The glass cleaning agent is just used for cleaning, not to form a surface for the collodion to grip. A dirty plate will have nuclei where artifacts will build if the plate isn't immaculatey clean and those areas will cause problems. When you roughen the edges of the plate, the collodon then has a surface to cling to. I use a whetstone to roughen the edges but you can also use sandpaper. I'd rather not have my hand rubbing paper against a sharp glass edge. Sharpening stones are fairly inexpensive.

Not all salted collodion formulas are so fragile that they rip easily. The ones without cadmium salts hold up better during processing although normally you wouldn't have a problem, especially if you subbed the edge with albumen. But the other formulas don't have the extended shelf life a cadmium-based collodion will have. Formulas containing potassium salts only are probably the least likely to rip IME. I've also recently read that the Ostermans don't recommend air drying the plates at ambient temperatures. They use a heat source (alcohol lamp IIRC) to immediately dry the plates after final washing. Apparently the slower air drying has a tendency to make the collodion shrink thus leading to it ripping after processing.

If you get plates that look out of focus with the Brownie, remember that the film normally is located above those rollers, not between them. I don't know if that will be a problem for you, but I've epoxied aluminum corners in mine to help keep the focal plane as consistent as possible.

I think John Coffer's book and dvd set are the best available although I have not seen Quinn Jacobson's new book ("Chemical Pictures"?). I would rank his original volume right after Coffer's. The Osterman's have a good chapter in Barnier's "Coming Into Focus" book.