Morini to start off with is cool if you are confident you know what you are doing and getting into, if you are just getting into it its a china motor kit is a better starting point because you can learn what is up in an affordable and complete manner, it seems each bike I build I do something different and better with each one. The mornini engine is more expensive and does not come with any sort of kit to mount it to the bike. You have to source/fabricate all that yourself
Overall, it builds a foundation of knowledge and is cheaper to start with a china engine kit, and it would suck to screw up a expensive engine like a mornini just due to beginners luck.
You can get the bike all solid like you want it and then swap in a mornini, the engine is a small percentage of building a MB, there are many other components.
Like, That's Just my opinion man.