I'm not a penguin fan, the only hob
filters I use/recommend are aquaclears. I run 2 110's on my 90 gallon tank, though it depends on how heavily you'll be stocking.
Pool filter sand is easier to clean/maintain than gravel IME, only thing is the color selection is limited...
Plants depends on how much time, effort, and $$ you want to put into the tank. If you plan to use CO2
and 2.5-3 wpg
the setup and light fixtures will be rather expensive. That also depends on your stocking, some fish will happily eat anything live and green.