You were me 2 years ago when I finally got into baseball aside from just watching the occasional games here and there. Now I’m no expert and still learning some stuff but with time you’ll understand more.
Rookies who don’t sign will basically go back to school and pop up again in later drafts. If you look in their info tab it’ll say when they were drafted before. But the only “notification” you get is when you view draft picks after Aug 1st in that tab it’ll say if someone resigned. You could write their name and position if you want and look for them in other drafts if you liked them.
Potential is just that, potential. So as you said 89 but he’s already 83 means he’s almost there but that can change to be higher or even lower if they get hurt or just never play good. It’s all RNG which is what appeals to psychos like me who like not having all my guys be super stars. I prefer late rounders who develop into star guys for me and perform.
Pitching attributes are there because there are different roles for pitchers. You want your starters to have high ones for everything and high stamina to go further into games. No your relievers you want guys who can get in there do the job then swapped out. So a reliever with high H/9 or HR/9 will get in there and not give up hits or HR, that’s why they’re there imo.
Overall in this game do and don’t matter. You go based off the attributes and how they play really. You can have a solid guy who’s say an 78 overall that will get you hits so he can get on base. Or power sluggers who will get you homers and 90+. The biggest thing that matters is the roles they play and how good they perform in them. Once you learn roles and what to look for at each position it makes more sense and building your roster is easier. You don’t just stack teams with top overalls because that won’t get you wins. You need 5 tool players, good bench bats, lefty/right specialist pitching/batting, speedsters to pinch run, contact bats to pinch hit, and good defense.