Gas Station is a business idle game: you start with a run-down forecourt and build it into a proper operation — more pumps, a bigger shop, staff to run both, and the cash turnover that follows.
The loop is the familiar tycoon one, and it's well paced: each upgrade visibly increases throughput, and hiring staff to automate a task is always the satisfying purchase.
Automate your own bottleneck. Whatever task you're spending the most time doing yourself is the one where hiring an employee pays back quickest.
Yes, once staff are hired — that's the point of the automation.
Yes — a light browser game with nothing to install.