A hydrostat transmission is best for utility jobs where changing speeds and reversing are the most important feature. They are far less efficient than a gear transmission for outright pull or fuel efficiency. For a steady, long term drawbar pull like plowing out in a field, they are not a particularly good choice. Quite a bit of horsepower is wasted.
But once you get used to it and for what you likely will use that tractor for, you will love it.
I'm not sure what the mechanism for protection is on the smaller hydrostats. On high horsepower ones like on a combine they can either have a high pressure bypass or they can have a mechanism to destroke the pump at stall pressure. But those are applications where the engine is supplying lots of horsepower elsewhere and the hydrostat is not designed to continuously handle full engine power. On these small ones, they may just be made robust enough to handle full engine power and not really have any over pressure relief. If you can kill the engine, it likely does not. If it stalls out while engine is at full rpm, it likely does.
If you expect it to do everything your significantly larger tractor will do in all applications, I think you will be disappointed. But used as the size tractor it is for utility jobs, I think you will love it.
As far as engine rpm, doing utility stuff and most loading jobs, I run about 2/3 throttle. If you need full power at the wheels, obviously you need to be running full throttle. About the only time I run full throttle is when I am mowing or tilling where the pto needs to be up to speed for the attachment to run properly.
