2 how-to questions

Is there any way to knit stripes into garter stitch without there being a right side and a wrong side?

i need a video that explicitly explains how to join mitered squares into a blanket or scarf, and how to actually knit the mitered square. Not large squares, medium sized. I’ve browsed so many videos on youtube, I don’t know which to pick. Any help would be appreciated.

I’d like to use a size 8 needle, or 9.

Stripes in continuous garter stitch are going to have a right side and a wrong side. Each one looks good but there will be a difference.
This is a nice video for mitered squares that takes into account the direction of the diagonal miter. It’s a join as you knit technique that avoids seaming at the end if that’s an alternative for you.

It may be one that you’ve seen. It has a reference to a basic video for mitered squares too. The size of the square depends on the sts cast on. One half the cast on sts will form one side of the square. Using a worsted weight or aran weight yarn depending on how tightly you knit will work with size 8 or 9 needles.
Sometimes you just have to pick a video and give it a try with your yarn and needles. Then you can adjust the size square from there.