We actually recommend no longer than 100-110ft. While it is standard RJ45 ethernet cable, it works with analog signals as opposed to digital so the length restriction is shorter than a typical ethernet network.
You can certainly use a lower MAX setting than 30. Whatever gives you full grate of fire without pushing burning coals off the end. It is not an exact science, unfortunately, manufacturing variances in the motors, stoker mechanisms, etc. can lead to sometimes significant variance in the MAX setting you will need.