As for what weight to bulk to, shoot for 170lbs and see how your body responds. As long as at least half of the weight gain is muscle (pretty easy) you shouldn't go past 15% bodyfat.
If you do reach around the 15% mark, no worries, just do a little trim down to around the 11-12% mark again by gently reducing calories (most can do this easily without losing muscle, or drastic calorie restriction, and sometimes without any cardio).
If you still remain lean (not far past 12%), congratulations! Pass go and collect 200 (in other words, carry on bulking)
I don't normally pull numbers out my ass like that ^ but it's good to have clear attainable goals.
Food doesn't matter as much as you probably think, muscles don't recognise "clean" diets; they understand total calories and protein Shoot for at least 155g of protein a day. Calorie wise you're probably looking to eat AT LEAST 3000 cals per day...you likely will have to increase upwards from there. Everyone's metabolism is different, but one thing's for sure, if you're not gaining weight (e.g. 2-4lbs/month), you're not eating enough.
If you haven't gained 15lbs in 6 months, give yourself a kick! lol
Can't comment on the Thyroid issue, sorry (be careful about internet diagnoses)