Can anyone tell or direct me to info about what determines a Catagory (FIDE) of a tournament?
It’s a rather manual calculation of average rating broken up into 25 point chunks. It starts at 2251 for regular tournaments.
See this page, section 0.5.
Appreciate that. I hear and read about Cat 14, 19, 20, etc
Here is an interesting article about estimating the strength of tournaments before ratings and categories. To my knowledge, Category 21 (average rating between 2751-2775) is still the upper bound in the rated era.
Given the lack of players who have ever been rated over 2800 (Kasparov, Anand, Aronian, Kramnik, Carlsen…if there are more, I can’t think of them offhand), Category 21 is about the best one can do…unless one can get Kasparov out of retirement. 
It is possible that several of the old Soviet championships were as strong or stronger than the tournaments listed in the Chessbase article. When the entire elite was marshaled to play in the championship, world title holders vied with other past world champions and candidates for the crown for the measly prizes offered. A tournament that could have Botvinnik, Tal, Smyslov, Spassky, Petrosian, as well as Keres, Geller, Korchnoi, and other titans is a murderous playing ground.