OK guys!!! RELAX!!! BREATH!!! It's OK!!!! STOP PANICKING!!!!!!! I use the 3M double sided scotch tape on a roll and put it in a dispenser, because it is strong and I like it. IF YOU don't like it!!!! That is OK!!! The tape runners I have found do not work as well on this project, for some reason, and it may be the paper bag, they just don't hold well. My second choice would be the double sided sticky tape, AKA art runner or whatever you want to call it. Just use this for adhering your pages to your book. You can use your tape runners for everything else!
As for the size issue, yes, as I have said before, some of the brown bag will show. That is OK, it is part of the charm of the book. If you don't want it to show, you will have to alter the size of your pages. Just be careful, because the inside pages tend to bend when the book is opened and closed. I usually add another alternating paper or cover with a picture or embellishment. Use the large sheet and tape down close to the edge, so the inside is where you will have the paper bag showing. Unless you want a boarder on the outer edge, then you can move the large sheet over cowards the middle more. This will cover more of your paper bag. Again, just be careful not to go too close to the inside of the book, otherwise you will just get bent pages. (Been there, done that!)
As for doing your pages first then putting them in the book, that is fine!!! If you are using brads and stuff. Go for it! It would make it easier than double matting!!!! It may make it easier working on your pages that way, since you are working in a smaller area. I quite frankly have never thought of this!!! I always did it the hard way!!!!

See we always learn new things with more people!!!!
Just remember, I don't want you to get frustrated!!! I am mealy a phone call away!!!