Okay so i've started a nano reef this year but previous to this i had a 800L freshwater tank but after getting a nano reef running i want to make the 800L tank saltwater but the problem is i had already bought a lot of the hardware that i would use in a freshwater tank.
Ive got a stand already but the tank has to be custom made because of the dimensions of the stand, so i havent got the tank just yet but the size should be...
180cm (long) x 90cm (tall) x 50cm (wide)

the hardware i have already is:
1 fluval 405 canister filter (1300L/hr)
2 aqua one power filters (2000L/hr) aqua one lol, well havent had a problem with these before
1 jager 60cm long 300W heater for up to 600L, if need be i can get another heater because in winter it does get cold, havent seen what effects the summer has on my nano reef yet.
6 foot T8 reflector with just 30W aqua glo bulbs (bulbs can be replaced if need be)

any need for a protein skimmer?

so im not sure how to go about this, what to use in the chambers of the canister and power filters, lighting upgrade? etc.

plan on just lots of base rock with a lion fish or an eel? or something else that would be okay?

LMK if you need more information, thanks for any input