well thoughts?

Well this week marks 2 weeks since owning my midas blenny, and my lfs is gonna order a mccostker's flasher wrasse thursday, just so i can see what they look like in person, im tempted to buy him thursday and put him in my tank friday, but ive adding 4 fish already in my 55 gallon, 2 weeks apart each fish. So im still undecided, my gut is telling me to go ahead and buy him, but then part of me is telling me, i have 4 fish, see how they do for a good month before adding a new fish already. So any thoughts on this. Levels are fine in my tank, just get worried about always adding a new fish, might stress out current livestock or bring parasites. What would you do?