buy prawns, RAW from supermarket. asian or normal supermarket, they are relatively cheap, on sale you can get them $10 to 13 per kilo, you feed half a prawn, dont feed too much as they digest pretty rapidly, meaning your water will fowl if your filter isnt up to it.
so just half a prawn, when you can see some food bumps in the belly thats all good.
temp , i suggest 25 to 28. i keep mind 28 to 29, hot days even 30.
but generally 28.
prawn is good, cheap j ust dont ever feed it cooked prawn!!
as for size, it will get big, if you can get your fire eel to 36 inches, i will drive to tauranga and take it from you and adopt it :thup:
it will take a couple years estimated for a fire eel to reach that size, probably more and some never reach that size, its not as easy as it sounds to get your fire eel to get to that monstrous size so i wouldnt worry yet.
if your tank is lightly stocked, 250 to 300 litres should be ok, just give big hiding caves or pipes, will be alright!