maybe when they are fully grown after 10-15 years they will need a 6 footer. they grow very slowly. mine are about 3inches & have plenty of room in their 3 footer
i have a similar (better IMO) filtration system in my sunsun tank. I buy bales of wool from my LFS. they are about 2400x1200 & last for 5-6 months. they cost about $13.
i guess any temporary tank would be ok for breeding over two foot. they like to lay on smooth verticle surfaces near the top of the tank. mine lay on the filter power head & any leaves of plants that are near the surface. i have seen pics of breeders that hang slate from the hood then remove them away from the parents. mine always eat their eggs on the second day.
Flourish excell is a fert that has the side effect of killing algae. I had BBA bad, was recommended her to use excell so i did. on the second day the BBA turned red then white on the third day & slowly disintegrated into nothing over the next four days.
im sure if you can maintain room temperature with a fire or gas heater that will hold the temp to. my tanks are in the lounge that has fireplace, cold nights when the fire is on the tanks will go up to 28' sometimes.
i had problems with my arognite growing algae until i added another big filter, now the algae is reducing so it may have something to do with filtration.
it will be constantly heating which will reduce the life of the element, you should get one that is suited to litres you have. just see how low the settings will go & if that suits what you need.