Beginner: Hand-sewing a decent seam Sewing Machines Parts and Sales in Los Angeles

Hello /r/sewing!

I’m basically a complete beginner when it comes to sewing, with the exception of a home-ec class I took about 15 years ago that I remember very little of. I don’t have a machine – I’m excited to make some things completely by hand! I’m currently working on a simple fleece onesie, and until now I’ve been using what I’ve since learned is a ‘blanket stitch’ on the (inside-out) seams. The blanket stitch seems to work fine, but as I read more about sewing it seems to be a more aesthetic stitch than what is usually done. I want to learn some best practices for hand-sewing a seam.

So, here’s a bunch of questions!

• What stitch should I use to make a simple seam between two pieces of (inside out) fabric? Does this change when I’m using fleece compared to other fabrics?
• Should I use a ‘double-thread’ or a ‘single-thread’ (I’ve always used single-thread but someone mentioned using double)?
• Is seam finishing important and should I be doing it? When is it appropriate to do (or not)?
• Is it enough to loop the thread through the fabric a bunch of times when starting or finishing a particular thread, or should I be doing something special?

I appreciate any advice I can get – thanks!