The simple answer is you just can't know for sure.
What do you know about the service history? That would tell us a great deal.
Depends upon your reliable vs. cost tolerance too.
I'd at least recommend the ET and hoses, but not call a full coolant system replacement a mistake. The more you spend, the higher the 'bulletproof' factor.
Test the pulleys (all three) to see if any need replacement. Replace all three at the same time even if only one tests bad. Check condition of the belts.