Yes variable power would be good as you could use it to make the amp key up to the proper power level of about 50 watts max carrier on AM. PEP wattage should be about 8-12 watts or so. On SSB you could most likely get away with 12-20 watts PEP max. If you don't want to mess with variable power, get your dead key set to about 1.5-2 watts max carrier on AM. It's hard to tell how much power is needed to get to the 50 watt max key up wattage on AM. But from experience with my amp, about 2 watts swinging to about 8-10 watts worked well for me on AM, and about 12-15 watts on SSB. Like I said earlier the key is to not overdrive the amp. Good luck and have fun with the amp. And again, make sure your antenna system is 100%. Get it best you can before adding the amp in line. Remember garbage in equals garbage out. Keep it clean and mean!!!!
73 and God Bless