depending on your budget and mechanical ability there are many ways to go.
I believe many members would agree that building the first one has a learning curve so keep it cheap and simple at first. after you have the hang of it pawn the cheap one off on the wife and build what you want after.
My experience was just that i bought a inexpensive kit and the cheapest cruiser bike i could find i had a running motored bike for under $250.00 you could find a used bike for less but under power i wanted the new parts.
Looking back I wish i had taken the time to build frame up. using a steel back wheel and large diameter spokes but the stock ones are still holding up.
With the shifter kit available you can go crazy but a 23mph or so stock engine kit on a bike is loads of fun.
Welcome aboard and good luck be sure to post pics even before you start. Simple hand tools can get you going and anyone can can do it.
IF it starts but dies soon sounds like you need to adjust the fuel flow. Easiest way is pull the throttle cable up on the carb and tighten down the screw so it is getting more gas. If it just won't light off, Try it with the kill switch disconnected first. If that is the problem might just have the wires wrong.
In chat you said it would start but dies fast, so I may not be following you correctly.
No worries, you will be up and motorized bicycle riding soon!
You may want to check for vacuum leaks as well, if you can keep it running long enough...spray some wd-40 where the intake goes into the cylinder and where the carb goes into the intake. If the rpm changes, you know you have a leak.
a properly adjusted throttle cable is key to getting it to idle. There should not be any "slop" in the cable you can adjust it both at the carb and at the handle bars don't make it tight just should have a little tension on it.
Then try adjusting the idle screw on the side of the carb turn it in a couple of turns and see if it starts to idle adjust the screw again once it is warmed up.
If no help there make sure your carb is tight on the intake and not leaking air in. also check the intake at the motor to be sure the gasket is sealing.
Just getting it to start is 90% of install the rest is just tinkering until you like how it runs.