It's your quilt, so it's your unique design. I usually go based on the pattern for the topper and what type of backing I use. If it is a solid backing, I stick to one color. As for the need to hand or machine stitch, I do them both a lot. Will do hand stitch applique work on squares and then machine sew the rest. So do what YOU want to do.

many many quilts are hand quilted in some areas and machine quilted in other areas...and are beautiful! it's your quilt

Does anyone have any advice to my question on backstitching? Not sure if this is a good method if my quilt block pattern is smack in the middle of the quilt.

What you can do is just do a few super small stitches in one spot to "lock" it in vs. backstitching. Either set your machine to '0' length, or just hold it in place for a couple of stitches. It's a much cleaner look IMHO... others might have a different suggestion though.

I would avoid backstitching. It really does show and often leads to some birds nests on the back. Starting with really tiny stitiches and slowly increasing your stiltch length is good. Another option is to leave fairly long thread tails then get yourself some self threading needles like spiral eye and bury those ends with a knot.

When sewing tiny stitches, how do I lock the beginning and ending stitches?

No need to lock really tiny stitches. Several in a row of teeny tiny are pretty much self locking, they just don't come out, which is a real pain should you decide you need to take them out (ask me how I know). I am talking tiny enough to not even be able to get your seam ripper into and darn near impossible to get a pin or needle under. They don't come out on their own when they are that small. Even yanking on either the top thread or the bobbin thread with tweezers they tend to not pull out. You only need about 4 or 5 stitches. Often what I do when machine quilting on my DSM is take a few stitches, increase the stitch length, take a few more stitches then increase the stitch length again. If I am FMQ with the feed dogs down I just barely move the fabric sandwich for the first few stitches then FMQ normally.

Thanks so much for the great advice! Will setting about 20 stitches per inch suffice in locking these tiny stitches? Should I still clip the beginning and ending threads close to the fabric?

I have a bernina so the stitch length setting doesn't equate to SPI. Give it a shot on a practice sandwich. I would test by doing a few stitches on that setting then take the sandwich out and try to pull the stitches out.

Yes I often will just clip the threads right down to the quilts surface. But many people bury them.

I have done both in my quilts for years. I have a couple of sew and flip quilts I did many years ago, after I got the top pieced (it is quilted at the same time) every thing trimed and even binding on,ell I decided it needed more so sat down and did lots of hand quilting, really liked how it turned out.