500 for a complete setup is very reasonable...if the seams are a concern you can either reseal it yourself or see if your lfs offers resealing at a reasonable rate or replace the tank itself to go with all your new equipment.I personally have redone plenty of tanks and it's not that bad if you have the time and patience
leaks and cracks happen on any tanks. I had a almost new 29g I bought cracked a few weeks after I bought it new. And I've heard of new tanks bought new leaking although it's a rarity.
I say go for it. What can you do to keep leaks/cracks from happening? be careful with it. But you'd want to do that with any tank whether it's 2 years old or 10 years old.
Go look at the if its in good shape get it.Worry about cracks/leaks when it happens.I know of a few tanks that have been running 30+ years with out leaks.
The glass in some of the old cathederals and castles in Europe is over 600 years old. Glass does not retain stresses from elastic deformation, and it does not plasticly deform. If the glass was properly annealed at the foundry, it will be as strong when it is 100 years old as when it was a week old. Since it made it to eight years without breaking, there is no question that it was properly annealed.