Don't try and share the "shared line". All internet feeds are shared -- you never have a dedicated link from your machine to the server. However, their "shared line" means that they know you will, 99.99% of the time, never use anything close to 1Gbps, so you are probably not close to a 10Gbps+ line. The "dedicated line" is probably closer to a 10Gbps+ feed.
You didn't mention IP addresses, but you'll need some IPv4 addresses which aren't cheap any more. You'll need these because someone in your building will be downloading pirated movies or something more serious and you want to be able to prove that's not you.
You'll need to be able to answer calls for problems 7x24. People get all bent out of shape for some reason when their Internet goes down or their videos start pausing.
If you get a 1Gbps feed and you share that with 10 other people at 100Mbps each, you'll have no issues. If you share it with 10 other people at 200Mbps each, then you may have complaints when their speedtests don't hit 200Mbps every time they click it (and they seem to do that a lot as they don't understand that they are being sold a max not a min).
All this assumes that the contract with the provider allows your resale of the product and that you have a way to distribute the Ethernet in the building.
Finally, my ISP doesn't inject anything in to user sessions or use any other scummy tactics, but consumers don't care. They all seem used to trading their privacy for some perceived value. They want reliable Internet (few outages, no pausing in their video, good VoIP) and good support. Most will have issues with their WiFi which you'll figure out, suggest a WiFi solution for them, and then you're supporting it for all time.
Such a correlation is difficult to draw from that single data point. You could look at the entire business model to get a better idea but in reality it’s not about that at all. Really it’s just what would the company have to pay to replace you? If it’s easy to find someone who can do the same job for the equal or lower salary then you have your answer.
There will be a range of salaries for your job position in your market. You should evaluate your total compensation against these to help you decide if you are fairly compensated.