"Per Player" limits?
Wow. That's really wanting microscopic control.
It could be done either way you suggested. SQL is probably better for more than, 5, in my opinion.
How many different players could you see wanting different limits for?
Less than 5? Less than 10?
More than 10?
Among those <x> amount of players, would they all have the same server/ulx access/command levels?
If the same, and less than say 5, I'd just make 5 new groups, set UnoLimited to allow certain prop amounts for each group, then add each player to that group.