Rick you will get very differing suggestions as line tends to be something anglers never agree on.
My tenpennyworth is use a good quality nylon such as Big Game from Berkley or Berkley Iron Silk on the spool.If you are casting baits out have at least 200yards of line on the reel.If you are rowing baits out then 400 yards.You can use a cheap line to bulk out big spools.I would use a line of 20lb test the reasons being 1. big hard fighting fish 2. tough as old rope ,rocks etc in the river 3. you're fish should not be line shy.
I would not use braid as cost of replacement would be prohibitive , braids are not abrasion resistant which is why anglers use 30 to 80lb braid as a replacement for nylons of 12 to 20lbs.Playing a 50lb Carp on braid would be a very scary situation!. Good luck.