I wouldn't call either of those fish delicate. Stock with 6 harlequins now, measure your water parameters daily, until you're sure the tank produces nothing but nitrates. Then add a group of corys if you want.
Would a total of 7 harlequins and 5 corys be all right? My lfs has panda, bronze, albino bronze, peppered, julii, and sterbai corys. I haven't decided which species to get yet.