1) Is the original address I've been using good indefinitely? (I'm not making any outgoing transactions).
It is good as long as you have exclusive access to the private key. If you lose the private key (contained in the wallet.dat backups you made), or if someone else gains access to that private key, then the address is no longer good.
However, you may want to consider generating a new address for each transaction, or at least every once in a while. If you use the exact same address every time, then anyone that sends bitcoins to you at that address will be able to determine exactly how many bitcoins you control. Do you really want to give up that much privacy? If those bitcoins become extremely valuable in the next 10 years, do you want to risk that?
copy and pasted my wallet.dat to a few usb sticks . . .
2) Will I be able to restore my wallet using wallet.dat in 10 years or so (or could the ability to restore from wallet.dat go obsolete?)
2) Will I be able to restore my wallet using wallet.dat in 10 years or so (or could the ability to restore from wallet.dat go obsolete?)
I'd be more concerned about those USB sticks going obsolete in the next 10 years or so. It would be difficult (though not impossible) to access today data that was stored on a 5.25 inch or 3.5 inch floppy disk in the past. I'd also be concerned about the data in the USB decaying over time:
https://en.wikipedia.org/wiki/Data_degradation
Quote
Solid-state media, such as EPROMs, flash memory and other solid-state drives, stores data using electrical charges, which can slowly leak away due to imperfect insulation . . . frequently, by the time the user discovers the data decay, the master data may be lost.
