Gear will vary depending on mowing conditions. Hi first or second would be a good starting point.
#3
Fish
The throttle should be Full Throttle, then you pick your ground speed.
#4
tom3
On my old GT second is too slow, 3rd is too fast. Both in final high ratio selector. Main reason I bought a hydro drive John Deere to do the main mowing. But I like the old Sears machine.