the only stupid question is the one you don't ask...
that said - you're asking us to design/pick for you. You need to do some more research and give us some more detail if you want to get help.
1st - i would start with a calculator that gives you speed info and gearing. My typical setup would be 13/14t (motor) / 36 or 40t (wheel) = 13/36 o4 13/40 etc. You will need to know wheel size, motor KV, voltage of battery (6s/8s/10s/12s), plus gearing (14/36) to get an estimated top speed.
2nd - Are you going single motor or dual motor? I would usually decide depending on rider weight. Greater than 80~85kg / 175-185lbs it might be advisable to go dual motors. Especially if you want to go up bigger hills regularly or want very fast acceleration. I usually suggest a single setup to start for simplicity, and less $ to start. Realizing that if you are actually limited, or just want to be faster (off the line - acceleration), you can add a second motor later.
If you go a single motor i'd also suggest 12 or 15mm wide belt and gears (more contact area and less likely to skip). Also don't go below 13/14t for the motor gear (more gears in mesh = less skipping). On 9mm belts a 12t motor gear is nearly impossible to avoid skipping when braking. No matter how tight. my experience at least.
With those details and calculations now you need to pick components. A single motor mount - make it yourself or buy one from Enertion or DIYes. If you get a kit you will get gears and belts that fit to start. A good idea the first time. You can get belts later from other vendors (9 and 15mm are easy to source. 12mm a bit tougher).
so it's helpful to look at other's builds and figure out what you like. From motor mounts that will fit your trucks, or are adjustable enough on your deck. What kind of deck do you want? A rigid flat deck is easiest. Flex is doable, but you'll need to separate your batteries and controller front and back w/ a gap in the middle to allow it to flex. A drop deck is doable, but your motor mount is usually more challenging to get one that works. Simple to start would be my recommendation. A good stiff deck, without drop or if you *really* want drop go w/ a small drop no more than .5-.75".
So top down:
Deck - preference
Trucks - Caliber II's or Paris (caliber seem a bit more common on esk8)
Motor mount - depends on truck, and deck style (able to fit/adjust for clearing deck)
Motor - 50 or 63mm are common. 63xx where xx is the length - longer will only fit a single motor per truck (second would be via dual diagonal). <55-60mm is usually able to be dual rear (sometimes need some spacers to fine tune). KV is important! I usually do somewhere between 149kv-245kv. I would determine what voltage your batteries are - figure out gearing for the top speed you want, and then pick KV that works for that KV.
Gears - motor gear 13-16, wheel gear 36t or 40t(DIYes has 40, most are 36t)
ESC - Least expensive would be RC Car (not boat, not Heli) ESC like FVT/XERUN/etc. (you will need the programming card as well) and limit you typically to 6s or less. >6s you can look at some of the 8s RC Car ESC's (start to get $$), or go VESC (my preferred, but configuration is needed and a bit more technical to get setup right - not plug-n-play).
Batteries - I like two smaller batteries vs one bigger (lay more flat under board and "stealth") and usually cheaper vs one bigger higher voltage battery. Depending on your budget and ESC (how many in series (6s/8s/10s/12s) it can handle). I would usually do dual 3s 5000mAh 20c batteries in series for 6s, or dual 4s 5000mAh 20c for 8s. (or 3s x 3 for 9s, or 3x x 4 for 12s).
Misc - enclosures, anti-spark button or Loop key, "fuel gauge" LCD, Lipo alarms, etc.
I'd read up on other builds and start to narrow down what you want (also what you can afford - li Ion batteries (SPACE cell and similar) are really nice, but $$ compared to Lipo). Don't forget a charger setup for your batteries, and i recommend a single battery connector type for simplicity down the road.
Lots to learn - welcome and GL!
