Again without Arsenal, but off the top of my head:
Ingram Smartgun X comes standard, I believe, with an integral smartlink, GV2, integral Suppressor, and a removable folding stock.
I'd probably pull the folding stock and replace with a sling. It's not going to stack with the other mods, but really, you're gonna need slings going guns akimbo.
Knowing my GM, barring any specific rule forbidding it, he'd probably let me upgrade Gas Vent II to Gas Vent III for one slot and the cost difference. It's barrel porting, and while you can't remove it, or stack it, you can add more ports.
The remaining usable/stacking recoil mods would be Heavy Barrel, Personalized Grips/Electronic Firing, and Under-barrel Weight/Auto-Adjusting Weight. Each grant 1 RC, but Electronic Firing cost 2 slots, Heavy Barrel costs 3 slots, and AAW cost 4.
Under-barrel Weight can by added as a Accessory. I don't think any of the others can.
HV and a C-mag (100rnds) are each 2 slots.
About the best I can see, again, without AR in front of me, is:
Ingram Smartgun X
+Personalized Grip
+Gas-Vent 3 System
+Sling
+Extended Magazine, 40rds
+Heavy Barrel
+Under-barrel Weight
+Smartgun System
+Sound Suppressor
Pool: 22 (24) DV: 5P AP: - RC: 6
Alternatively, dropping the Extended Magazine down to 1 slot, you could do the following:
Ingram Smartgun X
+Electronic Firing
+Gas-Vent 3 System
+Sling
+Auto-Adjusting Weight
+Smartgun System
+Sound Suppressor
Pool: 22 (24) DV: 5P AP: - RC: 6
This gives you the same amount of compensation, but makes for slightly more expensive, stylish, quieter, more concealable weapon, at the expense of 25% of your ammo capacity.
[EDIT: Ugh. forgot to count the GVIII slot. Can't add it as a mod cause it's already integrated. Had to reduce Extended Mags to get beyond 5 RC]
To get additional ammo capacity, you could actually start with a plain vanilla SMG, mount GVIII as a Barrel Accessory, the Smartlink as a Top Accessory, and lose the Suppressor, thus freeing up one slot used by GVIII, giving you 40ish rounds, depending on the model of SMG you chose.
-Jn-
Ifriti Sophist