g4rren

The 50 mm Primes are good, but on a crop sensor body they give the field of view equivalent to a 80 mm on a full frame sensor. This will sort of limit you in what you may want to photograph (its kind of a portrait-y focal length, but not so suitable for travel/landscape). The STM lens is faster, quieter, and has a shorter minimum focus range, so I would say is worth the $20, optically it is the same as the version 2, so its kind of down to your budget.
 
I would definitely have the zoom since it lets you take photos of different things more comfortably but also grab the prime that lets you take higher quality shots when the focal length matches your needs.

Probably not necessary truthfully, but you can if you want. 

1. It's too fragile. I had to replace the back glass twice throughout the course of 3 month. Both involved the S8+ being dropped from the height of.....10 centimeters 
2. I can't use custom ROMs due to the fact that Samsung locked the bootloader for the US variants

Well the one with I5 8250u is the Asus X407UB, which costs 600$, whereas the Ryzen 5 3500u one is the Lenovo S145-15API and it's 500$. The salesman recommended the Asus X407UB because of the dedicated GPU lol. I guess he underestimated the Vega 8 due to it being an iGPU