OP, I'm not sure whether or not you're already aware of this, but you'll need to change trains somewhere between Pelaw and South Gosforth, because the Sunderland metro doesn't go to Longbenton or Four Lane Ends, it goes west at South Gosforth and goes to the Airport. You'll need to change to the St James via the Coast train, at some point.
How much leeway is there if you're late due to the metro? Because currently they're not that reliable as the stock is so old. There aren't problems every day, but they're regular enough that it can be a bit stressful if you have time constraints for getting into work. Nexus have been given government money for new trains, finally, but they won't be in service until the end of this year at the earliest, and it won't be all the trains, they'll add in the new ones as they're available.
Also, there are times when they have problems and they take a train out of service, sometimes for the whole route, but more often just the stretch before Park Lane or Sunderland station. If your station is before those and it's vital you are at work on time, then this could be problematic.
However, if you will be able to work from home, and it's a job you'll enjoy, then it's probably worth enduring the commute for up to 6 months if the final pay off will be worth it. :) By the way, you won't save any money getting off the metro earlier, whichever station you get off it's 3 zones so the same price.
Also, it might be worth checking out the journey and see if you can get a bus from the business park to Regent Centre metro station if it's a late finish. That will cost extra, but should be cheaper than a taxi or uber, and once you're on the metro at Regent Centre you can stay on it until Sunderland. :)