I am drafting for a baseball dynasty league where you draft 10 minor league players and 26 regular players with 9 players on the reserve, what round should i start taking top prospects? and any advice for drafting minor league players?

Are you gonna be doing your prospect draft via msg board?

Nope its all just one draft, then you keep like 30 guys every year i guess

I would suggest going for guys like Machado maybe in the 3rd or 4th, Profar in the later part of the first 10 rounds. but don't draft more than 2-3 rookie hitters, if not you won't even be in contention this year.

Also you cannot pick up minor league players during season they are saved for the following seasons draft, so you have your 10 minor league players all year

I don't over-rate young hitters much more than what a normal draft is. A guy like Machado, I wouldn't touch until round 8-10 or so depending on what players are available. More often than not, Machado is either never going to be the player people think he is or it will take him a few years to become a top guy. Winning this year is just as important as trying to build a winner 3 years from now.