First, don’t go for the single motor kit. Buy independent parts and do it yourself. TRUST ME. I have no idea about longboard or electricity and I did it.
Helmet. You can go to your thrift store and find them. Or bike shop. If not, find something cheaper IMO.
Battery TWO 2s 8000 mAh. NOPE 4s won’t even turn your motor if I’m not mistaken.
Deck - just get a blank deck man and customize it if you want to save money because I saw your list and your missing a few thing. Like balance charger to CHARGE your batteries, threadlocker, power adapter for your balance charger. THE VIDEO I posted for you will give you a good idea.
Get a different remote controller if you want to cut down the cost.
There are more materials you need but if you get the stuff I show you it should be about $650.
Here’s my parts
6 zippy compact 3s 5000 mAh batties ~ $210
190 Kv - 90
VESC w/ male connnector - 102
Motor mount - 60
Pulley combo - 48
Remote control - 60
Blank wood deck - 50
Caliber trucks - 41 for both trucks
Flywheels and bearings - 28
Balance charger - 47
Skateboard screws for the trucks - 6
Adapter for your balance charger - 10
Grip - 3
Plus other accessories which is about 750 ish
You gotta be careful of which connector does your battery have because you can’t connect in series in a certain type of battery so you gotta get the series cable like the guy in the video. And it has to match the xt-90 female connect that comes with your vesc if you bought them off DIY.
So let me know before you purchase them because I can make sure you don’t buy extra shit like I did. HAHA