New SCID User Help -- Search Master Games By Position

Hi, Guys. I'm brand new to SCID, and frankly I find the interface difficult. (I'm sure it will feel seamless once I get used to it.) The reason I downloaded SCID is that I'm looking to create a collection of Master games that contain a specific position. (I want to use this as a study tool for openings.) Right now I'm learning the English Opening, Botvinnik variation. I'd love to have an easy way to play through games of strong players who used this opening, in particular to see how they move from the opening into a strong middlegame.

So, two questions: (1) What are the best sources of PGN collections of Master games [particularly older games, e.g., prior to 1950]?; (2) Once I create a SCID database containing these games, is it possible to search the database for games that include a particular FEN?

Thanks very much for your help with this, and I apologize if these seem like trivial questions. 

I have downloaded from here the biggest database ever https://lumbrasgigabase.com/en/download-the-scid-database-en/

It has hundreds of games from all GMs in existence, but not every single one of them i think