Welcome to the forum. As far as suggestions, you'll get plenty. There are 2 stroke people here along with 4 stroke and electric guys/gals who will tell you their way is the best way.
My advice is to start reading and find the information that you agree with the most. Your decisions will be based on the way you want to use your bike. Is it a fun time hobby, a daily commuter, or just something you want to experiment with?
These all will determine what engine/drive that suits you. There are many options to choose from. No one better or worse than the other. Check out the various sub sections of the forum for detailed information on the ways to motorize a bicycle.
Good luck. Have fun and ride safe.
Tom