Opinions on Build

Solution
The b450 tomahawk is a good mid-range "b" series board. I would go with it. Ryzen really scales well with high speed RAM, so I would definitely go with RAM faster than 2400mhz. I would go with at least 3000mhz speed RAM, and prefer 3200mhz. It may be a little bit more, but should not be too much.

As far as the brand, the 2nd generations Ryzen chipsets have improved RAM compatibility a lot, but I would still go with some of the bigger brands such as Corsair, Kingston, or GSkill. Those brands should have the most compatibility on Ryzen b450 boards.
The b450 tomahawk is a good mid-range "b" series board. I would go with it. Ryzen really scales well with high speed RAM, so I would definitely go with RAM faster than 2400mhz. I would go with at least 3000mhz speed RAM, and prefer 3200mhz. It may be a little bit more, but should not be too much.

As far as the brand, the 2nd generations Ryzen chipsets have improved RAM compatibility a lot, but I would still go with some of the bigger brands such as Corsair, Kingston, or GSkill. Those brands should have the most compatibility on Ryzen b450 boards.
 
Solution
I'd go with this:

PCPartPicker part list: https://pcpartpicker.com/list/sRGfV6
Price breakdown by merchant: https://pcpartpicker.com/list/sRGfV6/by_merchant/

Motherboard: MSI - B450 TOMAHAWK ATX AM4 Motherboard ($99.99 @ Amazon)
Memory: G.Skill - Ripjaws V Series 8GB (2 x 4GB) DDR4-3200 Memory ($87.99 @ Newegg)
Total: $187.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-09-27 13:06 EDT-0400