Welcome Retrax,
You did your homework. The Worksman Newsboy is a excellent choice for a bicycle.
I took it one step further and started with a bare frame and built a component bike (with Worksman wheels). I have mad skills and thought it would be easy enough. I soon realized there is a steep learning curve. Here is some advise:
Disassemble your new engine and inspect it, or have someone do it for you.
Use plenty of Lock Tite when re-assembling the engine (the entire bike)
Clean out your fuel tank before using it.
Expect problems and delays.
Throw away the spark plug and cap that come with your kit they will cause you nothing but problems. Your local scooter shop should have quality replacements.
Use quality oil and correct fuel oil mixture.
Follow engine break in procedures.
Continuously and constantly check nuts, bolts, and screws on entire bike. Everything all the time.
Have fun...