Welcome!
MB forum has an enormous reserve of postings/photos from builders prepared to share their experience. With 99% of the population having ample time on their hands courtesy of being locked-down indoors thanks to Corona Virus, now's the perfect opportunity to fill some of that time by referencing the forum's index. YouTube videos offer lots of advice too. We've all been there. Get searching.
Most MB builders start out with the common 80cc (actually 66cc) 2-stroke kit, then upgrade parts such as carb, exhaust, rear sprocket adapter, etc as they go. Plenty advice how best to go about this on the forum's pages. As with anything, learning on the job is the best advice I can give.
Get building - and don't forget to share your photos with the rest of us.