Converting My Old Tank

[Ebony951]

I want to convert my old Aq3 tank 52 litres / 11 UK gal or 13 USA gal and is and 15" Width, 15" Depth, 14" Hight.

Would this tank be ok to convert?
What do I need to add?
What should I get rid of?

How would I convert my tank Fresh water tank into a Marine Nano tank.

Please could you give me advice on how to go about adding the new equipment.
Thank you