I don't understand how a dealer can prescribe a needle size when s/he doesn't even know what size thread you're going to be using. A size 80/12 needle could be disastrous if you were using a 70wt thread like Bottom Line (or smaller) in the needle - nothing but skipped stitches. The same needle used with a 30wt thread or larger could give you a lot of shredded thread and breaking.
Match the needle to the thread you want to use in the needle. Set the tension on your bobbin case for the thread you're using in the bobbin.
Balance the tensions using the normal foot and feed dogs on a practice sandwich of the same weight as your quilt. Make sure that neither the bobbin or the needle thread tension is tight enough to cause puckers. Both threads should twist together inside the sandwich, not loop or lie flat on the top or the bottom.
When you have achieved a good stitch for normal sewing, lower the feed dogs (if you like to and are able), put the free-motion foot on, set the stitch length to "0" and try some FMQ on the practice piece.
Look closely at the stitches. If there are loops on the bottom, the bobbin tension is too tight relative to the needle thread tension. If the loops are tiny, either tighten the needle thread tension a tiny bit or loosen the bobbin a tiny bit. If the loops are bigger, you may need to tighten the needle thread tension considerably more and perhaps loosen the bobbin tension as well. Keep testing until you get a nice stitch.
If there are loops on the top, the needle thread tension is too tight relative to the bobbin thread tension.
You may not have to make any adjustments to the tension at all. Balancing tensions is not nearly as complicated as some dealers want to make it sound. And if ever a dealer told me not to ever touch my bobbin tension, I'm afraid I'd laugh.
