Xanzaba, glad you're recuperating well. From what I can tell, the old ones shouldn't grow back, but that doesn't stop new ones from forming. Supposedly they grow very slowly so maybe that should give you some time. They don't know what causes them for sure, but I'm sure there must be a reason you had 10! It's not unreasonable to think that it's related to your thyroid issues. I'm of the school of thought that these things are all related.
I think whether IUI or IVF is best is going to depend on what they think is the major cause of your infertility. I think IUI is the way to go if your hubby's SA is a little off and the swimmers need a little head start. They seem to do them as a matter of course for any one having infertility problems because they are less expensive than IVF. It can't hurt but those costs can add up too if your insurance doesn't cover them. If hubby's sperm count is really low or there are other problems with it, or if they can't find anything else wrong with you they will recommend IVF.
Some docs will offer you a laparoscopy if they suspect endometriosis. There are many different approaches they could take, so I'd suggest you research and find which one seems best to you, because when it comes to IF, no two doctors are going to agree on what is the best strategy.