I used to be able to see how many TSIs are still available for the membership year on the developer website, but now I cannot find it anymore.
Is it still 2 per year, or has it been recently changed to unlimited per year?
How many TSIs can I submit?
There is not a specific limit anymore. You should ask your question on the forums first, when possible and if there are no answers after a few days, you can file a TSI.
I'm glad to see how developer support changed in the last years, and now in particular. I think offering support on the forums that everyone can see and then allowing to request free support via TSI when the forum doesn't help is going to resolve a lot of the problems that I personally had with TSI.