There is no case ever documented that shows T3 screwing up the thyroid. Theoretically it should though.
But regardless, you should not touch T3 without any steroids as you will lose muscle pronto.
Clen people are starting to stay away from it as it is seriously getting linked to permanent heart problems - go to professionalmuscle.com and use the Search feature and read up on it.
When you say, hardcore, you mean non hormonal products? If so, Synthetek.com has alot of good nonhormonal injectibles that a natural can use, get good results, but without any hormonal sides.
Regardless, if you are 20%+, you should just do a good diet. When you are that fat (no offense, but that's FAT!), just a mild adjustment in yoru diet will give you results. Yod o a porper diet, you will get lean fast!