Couple of questions regarding 40 man rosters and young players

Before i start, first time buyer of MLB The Show and quite new to all things Baseball.

So say i have a young 70 rated player is in my 40 Man Roster.
I essentially have to start using them in the majors within 3 years of them being added on the 40 man roster because of the 3 Minor League Options?

I know you can remove them from your 40 Man Roster but chances are he would get picked up by another team because he is 70 rated with A/B potential?

As they are automatically added back to you roster during Spring training? Is this correct or is there something im doing wrong? As it would mean trading for and picking up prospects for future development pretty obsolete. No 6 or 7 years prospects developing in the minors.

I think the smartest thing may be to try and keep prospects that aren't MLB ready off the 40 man. The only way they'd get stolen then is the Rule 5 Draft which unless a team feels they can make an immediate impact they probably wont take them. I don't know what you can do if he is already on the 40-man.

They also have a few years before they are Rule 5 eligible.