The Tomahawk has a bios flash button so you don't need a CPU to update. You should be good there. Just follow the instructions in the manual. You basically just plug the mobo into the PSU , stick a USB stick with the update file into the proper port, press the update button, and let it do its thing. The tomahawk also has pretty good power delivery and heatsinks. This doesn't matter much on an 6 core but would come in handy if you want to upgrade to an 8 core eventually.
I would try to go for some B-Die if you can stretch the RAM budget up a bit.
https://pcpartpicker.com/product/wX...gb-2-x-8gb-ddr4-3200-memory-f4-3200c14d-16gfx
I'd also go for a different PSU. The corsair CXM 650 is a good unit in this price range. Corsair offers good deals on factory refurb units as well. I picked up one of these recently:
https://www.corsair.com/us/en/Categ.../Power-Supplies/RMx-Series/p/CP-9020178-NA/RF
You will also want a better cooler. I've built a lot of Ryzen systems. The stealth is not a very good cooler. The spire isn't bad but will likely be inadequate for the 3600x. It certainly is inadequate for the 2600x on stock boost. Your CPU boost performance is directly tied to your cooling. Obviously if you want to OC you will need a better cooler as well. The best value proposition is likely to be the 3600 manually overclocked with a $30-$40 Tower air cooler. This should easily outperform the 3600x on the spire for less money. This is somewhat of an assumption based on the previous Ryzen 5 CPU's but I'm fairly confident this will carry over to the new CPU's. Even if you don't want to manually OC, and decide the X chip is the route you want to take, a better cooler should give you considerably higher boost performance.
I'm assuming you'll be running lower quality graphics settings to boost frame rates. The 1060 will be a limited at high and ultra 1080p in most games and you'd get pretty much the same performance with an older Ryzen CPU.