You're on the right track. It's important to mask the extra light from the light panel. You can spend a lot of money on special glass, but before you do that I'd suggest trying a piece of plain picture framing glass.
I also highly recommend wet mounting. It's not difficult, and I find it gives better results, especially if your negatives have scratches in the emulsion. You can spend a lot of money on special films and solutions for fluid mounting, but you can also get the same results with very inexpensive materials:
* Gamsol Odourless Mineral Spirits (and similar products) are ideal fluids for wet mounting; they do not damage the negative
* Grafix Clear .003 Dura-Lar Film is a nice thin film that comes in sheets you can cut to size
* Any decent art store will have a semi-hard rubber "brayer" (a rubber roller) that you use to squeeze out extra fluid
Once you've done it a few times, wet mounting is quick and easy. The fluid doesn't harm the negative. When you've made your scans, you simply lift off the film, take the negative off the glass, and hang it to dry; I just leaded my 4x5 negatives against something on my desk.
https://www.largeformatphotography.i...ample-approach