Not that many with PA setups here I'd think....
1. Have no idea but seems it's old discontinued gear, used stuff on ebay in the neighborhood of USD 300 (the mixer/amp); don't see any prices for the speakers
2. Humidity and electronics aren't a good mix. Might think of desiccants or a dehumidifier? May not be a huge concern but that depends what you call humid.
3. Pro gear should be able to run full bore for a while I'd think but the older it gets the less I'd trust it to do so
4. With enough effort maybe altho probably not looking at the specs
5. Low volume shouldn't be an issue, you use as much power as you need for the spl you want (and with 98dB sensitivity, it won't take much to get very loud). Whether the speakers will sound good inside at low volume you'll find out soon enough.
6. Don't even know what that means to max out the computer
7. What do you want to do in the way of a crossover? The crossover for a subwoofer it says that is built into the speaker (which I assume already has a crossover for the existing woofer and tweeter)
8. No idea except don't drop stuff...
Good luck!