im currently running a 125ltr (2ft) marine tank. The smaller the tank the cheaper it is to run ie electric, water changes, top up water etc etc. But the water balance can change very very quickly if you dont keep on top of it, and this is when you can have tank wipe outs etc.

The big tank is easyer for a beginer, as changes in the water balance are less noticable due to the larger vol of water.

The start up cost is the biggest tho, Tank, Skimmer, pumps, Live rock, First salt water fill, full testing kits. Once you have past the year tho, its well established, and prity much will run its self with good water changes every week or 2.

I started straight into marines, but did the research first.

I go on Ultimate reef, great forum for info and help, and some bargins to be had as well.