If you have a concrete floor, then you can place it anywhere
if you have a wooden floor, then the best place is against a wall.
Heater
Best to go with two 200w heaters, for safety
if budget is tight, then go with 1 300w heater and place it by the outlet of the filter.
Filter
go with something nice an big, my preference is with a fluval 405
but I know of the aqua one 1200 external filter works well too. No doubt somebody will have other suggestions.
There is no single way in doing things, what works for you is best.