Hi and welcome to KH!
You're right, typically the patterns are for larger squares. If you're going to do smaller squares, it might be an idea to knit the blanket in strips, changing colors or stitches as you wish to mimic squares and then sewing the strips together. They'll look like multiple squares but you won't have to do so much of the dreaded sewing squares together.
Sizes and stitches to cast on will depend on the yarn and needles you're going to use. i think a gauge swatch with your yarn and needles will probably be the best solution.