Well with elevated thyroid antibodies (TPO=thyroperoxidase, TG= thyroglobulin) you should have been told you have Hashi's or autoimmune thyroiditis. I am immediately suspicious of any doctor who fails to inform their patient of an important diagnosis like this one
They are leaving you in the dark and that's bad practice. They should have spent some time explaining this and what it means.
Reese here is the real expert on thyroid nodules but my understanding is that FNA is indicated for any that are 1 cm or over. As far as scans, etc I'm not as informed on when these are indicated. Nodules and enlarged thyroid are very common with Hashi's and most time the nodules are benign but should be checked nevertheless.
Get your labs from the Dr's office. We've learned not to take "you are fine" for granted when told by nurses over the phone, and again they are not as forthcoming as I would like a doctor to be. Always get a copy for yourself and we can give you pointers on how to interpret them. Also we will need the reference ranges that are after your results because these can vary from lab to lab.
As you say, 25mcg is a very small starting dose. You will need to increase until your symptoms are relieved. Going by symptoms is more important than what labs show overall but most doctors are lab junkies and forget to watch how their patient actually feels.