I have used vinyl in bags mostly like you are doing for pockets inside a bag. For your application, the "thin" should work just fine. It is only to allow you to see what is in the pocket, and will not really be subject to the stress of say.....the weight of what is in the pocket pulling on the seams. Hope I said that correctly....The tips others have offered on sewing with vinyl is very good so other than saying clips are better than pins, I won't repeat. Here is a link to some zippered pouches I make that I use the thin vinyl in and it works great. And this binder that uses vinyl....for these thin is better.
https://atkinsondesigns.com/products/classmate-pattern
https://atkinsondesigns.com/products...gettes-pattern