You need to go buy drive roll kit KP654-3/64A. I used tweco heavy duty 3/64 tips. Both alloy wires work so its your choice. I used my Lincoln SA-200 as a power supply for the LN25. It seems to me that constant current from my Lincoln worked better than constant voltage from my trailblazer with alum wire. I welded 4 inch alum pipe that was used as buss at electric substation and it welded great, nice welds. Just dont let the wind take away your argon gas.
Lots of 'expert' advice out there on aluminum, most of it is just what someone read in some weld product catalog.
I use 1.2mm 5356 in my ln 25 interchangeably with steel wire.
If I did a lot of al., maybe I'd buy one of those teflon or nylon liners,but I have no problems with feeding .
As others said keep the gun straight as possible, use the minimum tension needed on the drive rolls, and things should be ok.