I gave you the classic autolyse process where yeast is not added to the flour and water at the outset. However, some people use IDY or a natural starter during autolyse on the theory that the autolyse rest period will be over before the yeast starts to kick in.
Unlike the ADY, there is no need to proof the IDY in water. It can be mixed in with the flour. Some bakers who switched from ADY to IDY proof the IDY in water out of habit, and occasionally a baker will proof the IDY in water to get it to start working faster. For your cases, it's perfectly fine just to mix the IDY in with the flour. As you noted, you don't need as much IDY as ADY. The IDY has more active cells than ADY and is made up of finer yeast particles. The IDY can also tolerate higher rehydration (proofing) temperatures than ADY, which promotes faster rising.