hi Jason
I used to have a 6foot tank in the lounge with cold water set up, it had a small shoal of rudd , two golden tench, 4 goldfish and 4 FI carp in it ,
other fish you could put in whould be swap rudd for orffe , and F1s for two
gost koi , though thay whould prob out grow tank, but local garden centers that sell cold water fish in spring usually have some good alternatives,
I tried to keep perch in a tank and found thay did not keep well something to do with a perches swim bladder being very sensetive, so do not advise you
to keep them ,
your tank should be fine run at room temp keep cheak on temp if you think its getting to hot do a 10% water change, that will drop temp of tank, remember do not use water straight from tap , unless you get a decloronator,
to treat the water, i used to have a water butt that i would keep filled with water so i had a good supply of fresh water ,should i need to do a water change,
I have now changed to a tropical set up, because i found there to be a
larger choice of fish to keep, and some real intresting fish once, you look past the usual guppys ect,
good luck Doughnut