In general is it more value to use my miles on my home FF program (i.e. Turkish Miles & Smiles; currently 70k Miles and Classic Plus status till 2023) or should I be exploring using them on Star Alliance partners as well? I am not very picky about the destinations i.e. it's not a particular city that I want to visit. For buying Star Alliance (non Turkish Airlines) routes using miles do I have to do this via the phone call center or is there a way to do this online as well?

Also, I see that the miles usage is only 2x more for Business than Economy. If I were a fare paying passenger this is typically 3x to 5x I feel. So in that sense is it always a better deal (relatively) to use miles for business than economy purchases?

Also, is it worth purchasing business directly using miles or to purchase a regular economy ticket and then use miles just to upgrade class (based on availability).

Finally, I see that the number of miles needed is sort of a flat rate agnostic to exact date and most destinations seem to be in certain bands (e.g. all of EU is approx. 30k miles for me with home airport BOM and connecting via IST). So are there any particular destinations which tend to be expensive to buy usually but relatively cheap using miles?

Since my miles don't expire till end of 2021 (TK recently extended the expiry) is it worthwhile waiting i.e. are there offers on miles from time to time that make them go further? Or not really?