2" lift should work, as long as you have a area to jog the torch to, where the plate cannot strike it while being loaded, and you can also change your tips out.
The higher the current, the cleaner the cut edge. There are other factors, yes, but you will get a cleaner edge on thicker metals with more amperage.
30 amps will cut 1/4 plate, but it will not be as clean or as fast as 40 or 50 amps, and you will be running at the edge of the duty cycle of that TD plasma, if cutting a large piece of 1/4" plate. You have three levels of cut quality with a plasma,
1.quality AKA genuine
2. good AKA rated
3.sever AKA snaggletoothed beaver teething device. Almost like a torch cut. (this is a bit of an exaggeration, but so is their advertisement
)
With that TD plasma,
1/4 is quality, 5/16 is rated, and 3/8 is sever.
It will cut 3/8, but it will do it rather slowly, and the edge won't be as nice as you would expect.
The torch tip should not touch the plate surface, but hover between .06-.10 off the surface, depending on plate thickness, amperage used, cut speed, etc.