I can't tell how much your specs have evolved since your initial post, but doesn't seem like you are cutout for the realities of DIY, at least at this time. I wouldn't usually recommend this, but maybe it would be best for you to get your feet wet with something that fits within your budget, but relaxing your requirements just so you can start off with ebikes. Something like this:
https://www.amazon.com/Macwheel-Electric-Advanced-Brushless-Teenagers/dp/B08D3T2H1S/ref=cm_cr_arp_d_product_top?ie=UTF8
Great customer reviews, and no mention of fires in the Q&A or the reviews. Cast wheels so you don't need to worry about spokes. Only minor assembly required and comes with tools. Rear wheel hub, and no need to worry about torque arms at this power level. Meets your range requirements with pedaling/PAS, light/transportable, battery included.
https://www.amazon.com/Macwheel-Electric-Advanced-Brushless-Teenagers/dp/B08D3T2H1S/ref=cm_cr_arp_d_product_top?ie=UTF8
Great customer reviews, and no mention of fires in the Q&A or the reviews. Cast wheels so you don't need to worry about spokes. Only minor assembly required and comes with tools. Rear wheel hub, and no need to worry about torque arms at this power level. Meets your range requirements with pedaling/PAS, light/transportable, battery included.