Chris,
Welcome to the board.
My best advice is to collect what makes you happy. It doesn't matter if 8x10s cost more or less than 3x5s. You should have pride in your collection if it's stuff you love. Who cares what it's worth. Buy what you love and enjoy it.
If you like the look of 3x5s with an 8x10, then go for it. Many like 3x5s and cuts more than photos as you get to choose the photo you pair with it. Compared to a 3x5 with photo, a photo of a dead HOFer will cost more and may not present nearly as nicely.
A few of my items, both cuts and photos, are in this thread. Others posted a few great examples of what can be done with some creative matting. Hope it gives you some ideas.
http://www.net54baseball.com/showthread.php?t=168495