Maxing out my Red Squealer...

Hi there. my Squealer is going along good in terms of stats, and here's what I have.

22 str
20-ish wlk
22 tgh

I slapped on two Vipers and two squealer AMs. I don't plan on giving it an 8-vulcan or even a zook.

Here's my questions:

1) What stat would I need more? I thought I should've raised str, but I heard tough was recommended due to the nature of rushing.

2) What upgrades should I get on the AMs? I'm debating between High Gladiator and Great Grappler.

3) I only have two more cart spaces, and I still have 3 carts I want to add. Which 2 of the 3 carts should I get?
- Cost Capacity
- Internal Weapon
- Boost Run

Answers are appreciated =)

1) Take WLK to a Boost Run breakpoint, then try balance TGH and STR, or, take STR to a breakpoint for your punch and max TGH, or vice versa.

2) *shrugs* I didn't see much of a need to put sub weapon upgrade on them.

3) Boost Run and Cap+.