when do I need a skimmer?

I'm setting up a 55g no sps and trying to spread out the cost / build parts myself.



I know to leave room in the sump for an eventual skimmer, but do I need to buy it right away? If not, how do I know when? Since your supposed to add slow, and I won't have any demanding corals for some time I'm guessing I can get away with water changes at least through the uglies?



Also, its confusing how the powerheads / return pumps / skimmer / headloss all play together. And the guides contradict each other ALOT. Any recommendations for reading up on flow are much appreciated.