Welding Tips and Tricks

i have a project coming up to weld out an aluminum tank.
the critical bits i will tig.
however toying with the idea with mig some of the longer runs.
aluminum is 3mm afaik but my mig is 180amp max. was looking to use a helium mig to increase heat output as i think the mig is a little underpowered (certain the duty cycle is, but i may borrow a commercial mig machine buts thats also 180amp).

any idea on what mix i should use (if any at all) ?
whats the cons of using helium mix?

I run a 75/25% Ar/He mix on my TIG and my Spoolgun. My Spoolgun is only rated for 135A with 0.030 wire. I have welded plenty of 3/16" (0.1875) with it successfully. On 1/8", its flawless. I have, with preheat and bumping, welded 0.25" but that was a small aspect of a job, and I was in a pinch. I definitely feel the He mix made it possible.

With Ally MIG, I always push whenever possible and only uphill on vertical. I find adding a few tacks intermittently along the piece really helps build some heat up so the initial weld doesn't have cold toes...