I'll admit I haven't bothered my head much with threads for the last 40 years or so, have done just fine with my Coats & Clark Dual Duty. When you read the old books though, even though they don't discuss things like seam allowance they always talked about the thread weight.
Starting when I first long-armed (close to 10 years ago now??), I found that the lighter weight thread bobbins were wonderful. We also found that we couldn't wind a good bobbin on our own and that it was just a lot easier to buy them prewound. Then I got better long fiber threads for the top stitching.
With my modern Bernina "sewing computer" my friend warned me it was rather fussy which is one of the reasons she gave it to me. She likes to do a lot of fancy stuff and mostly I just quilt and straight stitch. She said the machine likes Aurifil and I like it too.
I tend to use smaller needles and a smaller stitch size than many. I believe it is necessary for strip piecing which is how I mostly work. I find most machines are set with a too large stitch as a default, if you can easily pull away 3-4 stitches, it needs to be tighter. The downside to my tiny stitches is my declining vision, I just can't see small stuff very well any more even with my readers on. To help and since I typically work in scrappy projects anyway, I typically use a camel brown or slate blue-grey thread for piecing. If I need to take something out, typically I'll just recut it and restitch it but contrasting thread helps a lot!