I think some of your questions have been answered here.
https://www.themoviedb.org/talk/6442ced4d35dea02fcfb0fab#6442d4a0d35dea0455fb1a07
And the other part here:
https://www.themoviedb.org/talk/5d34aec717792c0011bc9bd9#66f1704a2d98d59ce13b0359

If I'm not being redundant and insisting, I would only like to state one question/doubt regarding rate limiting ----- what does 'connection' mean and if I fire 20 api calls at the same time are they treated as 20 'connections' ? while they are pending ( waiting to be resolved or rejected ), if a pending request is a 'connection' then clearly we can't make fire more than 20 api calls at a time as @ticao2 and @travisBell have said in one discussion that 20 is the max limit of connection. ----IF I got let's say 100 request to fire at once, I got to batch them in 5 batches of 20 right? and fire them one by one after the previous batch is done being resolved/rejected fully
AM I right ?
Please confirm
The matter of fact is -- I tried it myself, fired 4 calls, got 1 page each response, total 4 pages, 4*20 = 80 results, extracted ID from each result, got 80 IDs, stored them in array, fired the api call for each ID all at once -- 80 api calls were made at once, everyone of it got resolved all the way to 80th API
No error was found, or thrown by tmdb, I honestly don't know what to believe about LIMITS - IS IT 20, 50 or something else ( talking about the limit of request that can be live/pending/open-connection at once between tmdb and IP address )

I think it's best to focus your questions on a single conversation.
I suggest this one
https://www.themoviedb.org/talk/5d34aec717792c0011bc9bd9