You can start without a skimmer.
the prizm line is too small for your size of tank, and there's a lot of debate on how effective they are on any tank.
as for SeaClone, there's a 50/50 split on whether they're worth using or not. The 50% that like them have modified them to be more efficient skimmers (needle valves and airstones, etc...just minor tweaks).
If I could do it over again, I wouldn't have spent $90 on a Prizm Deluxe and instead would've bought a CPR bak-pak2 for $130.