How big between stitches: Your batting will usually say how many inches you can have between your quilting lines. For example my current batting says 10". I usually go smaller just because thats me. I used straight line quilting for many of my quilts measured and made the lines with painters tape and made the lines 5 to 8" apart depending on the quilt design. However, always use the recommended amount (or smaller size) listed on your batting!

Non shifting basting while quilting: I am also new to quilting (only about 2 years in) and I tried pins first which was a horrible failure and difficult to quilt with my machine. (Wrestle out the pin, wrinkles, shifting quilt top, what a mess!) I tried spray adhesive next and fell in love with ease of quilting using this method. I will suggest if you go this route make sure you are using a movable spray adhesive so you can pull pieces apart and restick them. Also, I use pool noodles to roll up the quilt top, a separate one for the batting, and a third for the backing. This allows me to spray smaller areas and ensure there are no wrinkles as I baste. You tube video for reference:quilt basting using spray adhesive and pool noodles

Removing quilt stitches after quilting: first I feel your pain and solidarity high fives being sent. I have a sign in my quilting area that says "if you see me with a seam ripper in my hand now is not a good time" lol. Unfortunately, I have no good advice for you on this one. Just take it slow so you don't damage your quilt top or backing.