Do Federal Pacific baseboard heaters have a reputation for poor quality?
The only problem I have ever had with FPE base board heaters is the thermostat. I am not saying there was a flaw. The contacts fail after many years of service and have required replacement. Your total of 5000 watts would be 20.8A so a 30 Amp breaker would be normal with #10 wire supplying them. If you cannot find a replacement thermostat (for the ones in the base board) I have added a wall mounted thermostat for the room and bypassed the thermostat but not the over temp sensor that is a safety if the contacts weld closed in the thermostat. Added Today I just did a power survey on an older 25kva 480 to 240-120v transformer that has been in use for? It wal lightly loaded at 54A at 240. I increased its load to 91A at 240 even ballanced loads (120) and it is still running cool on a hot day here (mid 90's) so I would still say FPE products other than "stab lock" are good.