#1 I can already tell you that you will be successful because you are asking great questions.
Aces can come from four places. The draft and IFA's, free agency, and trades.
Personal I like to pay a little extra and get them in trades and FA since I now no how good they are. I develop hitting and buy pitching, but to each his own.
Don't about the overall numbers all you care about are their individual skill numbers. Now obviously there is correlation, but the best player I've ever had never got above 87 and the best rp never got above 81. You want to focus on contact, power, vs. R, the most for hitters, and vs.R and control for pitchers. Obviously lots of the individual ratings will impact performance, but some animals are more equal than others. I often like to look at the top 10 guys I am interested in the draft, pretend they are real players, and then decide who to draft. Often the SP who is 85 overall looks like a #1 starter to me and the SS with an 88 overall who looks like a above average SS, but nothing special.
This is more than you asked, but you are doing fine. Butch Glauber looks to be developing into a very nice 3B who could start for the big league club next season. I don't think he should, just he could. Julian Cerveza doesn't have enough bat for me, but at worst he's a wonderful utility IF and a decent value for where he was picked. When it comes to IFA's, I won't even look at a guy I couldn't see myself drafting in the top half of the first round and therefore usually end up getting 1 or 2 bigger one's instead of smaller IFA's, though that 1b you got was a good value. Your pretty covered at SS now, but overall for a new owner you are doing a nice job of brining in talent.
If I was in your place I would link up with a vet and pepper him with questions. Scooter would be an excellent choice.