2nd year drafts & onward

I am new and have no idea how much is left to draft in the second year and after.
Of the the consensus top 6 at each position, what percent might be free to draft?
Of the top 15ish at each position, what percent is usually out there?
In other words, of the veteran mlb players, is it only the absolute dregs who aren’t kept or are there veterans to draft that you wouldn’t be embarrassed to start?
This will help me in second half decisions.