Up to you...in every respect.
I like to do a day at a time and I try to be as in tune with the day to day goings on as possible. General league stuff as well as team stuff. I'm not huge into playing each game, I personally prefer the GM role, but I do play on occasion.
I keep a rolling list of guys to target at each spot, at least as a backup in case a MiLB guy doesn't pan out or a current guy falls off. It gets tougher the more into the future you go as familiarity with current players trends to zero.
I do auto-Ai MiLB promotion/demotion. They know more than I ever care to learn.
Yes, I try to find guys from the minors on up to fit what I want from a manager.
Still learning about Scouting...that's tbd.
Otherwise I'd read most every thread here concerning Franchise Mode.
This one in particular...
https://forums.ootpdevelopments.com/...d.php?t=312931
https://forums.ootpdevelopments.com/...=312931&page=3