Hi LionFish,
Mine is a twenty gall plus about two gall in external cannister filters. It has been up about two months now. I have spent a lot on this so I feel for you being on a budget
Go with the softies - button polyps, xenia, ricordia, etc. I also like feather dusters - there are now four big ones and loads of little ones growing on the barnacles.
I decided not to go with an arrowhead crab due to the size in a small tank - "The size is variable, many reaching six inches, and some up to 10 inches".
I also decided against an anemone and a starfish at this stage as I want the tank to mature quite a bit more before I think it will be ready for these.
I have red hermits, astrea snails, cerith snails and peppermint shrimp in the clean up crew.
I'm sure you will be abel to get yours looking great, even on a low budget, just take time and save up for the important things such as lighting, etc. If you skimp too much on lighting at first you will only end up going back and buying more/better lights at a later stage.
Cheers, Eddie