I THINK the aluminum diamond plate I have used is 3xxx, but as it came from an industrial salvage yard, it is hard to know. The extrusions were 6061 T6 or T651. You don't bend the heat treated stuff. You can cut all of it with a Skill Saw and miter saw with a normal carbide tipped blade. 5xxx probably weathers the best, 5083 & 5086 being commonly used for aluminum yachts, and it is tough. I replaced a section of the floor in an aluminum dump bed with 6061 T6 [I think], it has been holding up OK for several years now. I prefer the way 4043 filler runs over 5356, and I usually run 3/64 diameter wire on 1/8 and over material. I usually run it a little short of spray transfer [shame on Me] but it has worked out OK. .035 filler is easier to handle, I am more likely to run that in spray transfer.
I adhere strictly to FC-2002, use materias from the salvage yard, and build hell for stout, as it only has to last for the rest of forever. Luck has been with Me so far...
If You plan to use the LN-25, You might keep an eye out for a short conduit strate gun. I use a spool gun, it works for Me.