My Limited
Experience over three engine installs is to be patient.
When I ordered my first engine, I had a list of items to do that was a mile long.
Fortunately, my typical procrastination turned out to be a benefit, in that by the time I received the engine and began to install it, I found most of the stuff I thought I needed was not necessary and overkill.
Besides, I had much to occupy myself with unplanned fitting and problem solving due to the frame I was working with, which called for some careful analysis before putting things together. I learned that simple is best.
For example, the dropouts were recessed cnc machined aluminum as was the frame seat clamp and I did not wish to mess up bike by rushing work. Amazing what a few SS washers and longer axle can do ... if you have the patience to work it out and wait until the right parts and tools are available.
Three bikes later (only two engines) I understand that these are bicycles and though motorized, need to be seen as not motorcycles.
FWIIW, I went from 25cc 4-cycle which I loved and ran great, but would not take me up my hill-street easily, to Tanaka 3300 which solved the problem and I like the light torqy motor and fast enough for a bike and me.
Take it easy and have fun with the project - one patient step at a time.
Life is short enough without increasing grief more than is necessary. Makes it way more fun.
BTW, Augi is right about the trigger throttle. Simple and works. And, I think safer to make quick stops, if needed.
Here is pic of variation using Sinz brake lever...