You’d need to accept uploads from others. That would be your ingress. You can’t serve data if your vaults are empty.
The way it works is you need to have them filled up and then you get paid for GET requests (when/if you get them).
Right, but you aren’t making anything until you fill it up as I mentioned above. But you must pay for bandwidth, operations and h/w anyway. Ultimately you’d get paid for GET requests, but not more than other providers (most of which runs vaults on crappy home hardware which costs a fraction of your hardware).
Another thing is you’d not only have to come online and have your vaults filled up, but also stay online for a while to gain reputation to get data and later read requests. I don’t know for how long, but again, it’ll cost you dearly in power and cooling before you see any SAFE coins being credited to those vaults.