indeed. p90 mags need p90 pouches. They are 10-15 for singles and the nicer eski ones are 30 or so for doubles. The condor ones sometimes are sewn too small and don't fit the mags without using force and usually that ends up breaking the plastic mags.
Don't play in the forest. Go play at red devil's in kemptville. Every saturday, gates open at 8 am.
I am a big guy and I can fit 6 p90 mags across my chest. Depending on how much you shoot, 6 KA p90 mags don't hold a whole lot of ammo for the space they take up.
You may or may not be able to mount p90 pouches on that chest rig very well. They need about 8 rows of molle in height for space. Will get you an exact number when I get home tonight. The best thing to mount them on is a zip up vest, though I've seen guys with 4 on a plate carrier that they wear a little higher on their chest, it just means you only have half of the molle weaved so they might be loose.
If you go with an AK or M4 the gear options get a bit cheaper/less specialized.
You will also need either a p90 sling adapter for that sling or you need a p90 specific sling. There is no where on a p90 to clip a regular sling meant for an m4/other rifle.
Leave the helmet out for now, buy a spare battery.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.