I convert T4 to T3 as well. I take T4 only (like Synthroid, Levoxyl, other brand names and generic levothyroxine) and am symptom-free.
We are all different. Some of us do fine on T4, some have to add some T3 to that, either synthetic or desiccated. T4 is usually what is prescribed first.
You want to be sure that your doctor tests you 4-5 weeks after the initial dose and 4-5 weeks after any dose change to see what the meds have done to your levels. Be sure your doctor is testing FREE T3, FREE T4 and TSH (all three) every time blood is drawn. When you get your test results, sit down with your doctor to review them, re-evaluate symptoms and adjust as needed. The guideline for FT4 is midrange, and for FT3 is upper half of range, but symptom relief is what's most important. Just because you are "in range" does not mean you will feel well. Some of us have to be well up in the range.
If you want help interpreting results or learning to interpret them yourself, you can always post them here with reference ("normal") ranges, and we'll tell you what we see and where we think you should go.
That is a very complicated question to which there is no clear answer. In the first place "synthroid" is a make-believe brand name. If you search the FDA site you will find, over the years, there have been significantly different chemical compositions. all with the same "brand name". Peoples reviews are not the best way to choose a physician. The exact mechanism that causes a problem is often elusive, even when you have a "top doctor". My advice is to seek a second opinion and try to ensure at least one opinion comes from the staff of a teaching hospital.
This depends on the person. I don't have any issues with converting T4 to T3 and take T4 only medication.