I think 2ndGearRubber is on the right track - very little will be controllable, but the data stream may be helpful. Frankly, I don't like introducing scan tools into the workflow with my students or apprentices until they can show me they need one. There are quite a few workarounds, saving both time and money, if you know how to read a schematic and have access to good ones.
If you want to go the scan tool route, I've had some good experiences with Topdon, specifically the Phoenix Smart and the Phoenix Plus 2. They offer plenty of "mid range" scan tools for pretty fair prices - if those tools use the same or similar software to the Phoenix lineup, I wouldn't have an issue recommending them.
My current aftermarket daily driver is a Matco MaxFlex Pro. The hardware costs about $2300, but, for the Flex lineup, Macto has forgone the traditional $1000/year software updates. Hot button issue, but they offer a monthly subscription to complete access to specific manufacturer's software. I'm a GM dealer tech, so I pay $16/month for access to GM software, and can buy a one month add on when I have to look at a Powerstroke or a Cummins. Constant software updates improve the tool at least a few times a week, and it hasn't skipped a beat yet. It does need to be connected to the internet to validate your subscription each time it starts up, which is annoying, but it will continue operating after you lose connection on a test drive.