Hi,

My tank is 36"L and 12"W... so if I was getting one of aqualights
systems or retrofits, 36" is the size I should be getting right?

If the answer is yes, all of the systems come with 96W bulbs.

And I would have an open tank. Not too keen on it but if it's an option
I will consider.

It's too much for my needs (either for plants and for my pocket).

Any chances of getting a 65W bulb in those?

What would you recomend, in an economic standpoint?
Not for the initial purchase but for energy consumption?