-Just do a 2x 16GB kit. Ryzen doesn't play as nicely with more than 2 dimms installed - I'm not saying that it won't work at all though - plus it's easier on the Internal Memory Controller.
-At least get a 7200rpm spinning drive. Some of your games, especially the ones that frequently access the drive, won't play smoothly on a slow 5400rpm model.
That's my 2 cents.
-16GB RAM would be enough. Get a 2x8GB kit. Ryzen likes high memory clock, so 3000+ MHz is great.
Do I see it correctly that you already have your SSD and HDD?
-Get an NVMe SSD instead (or get one in addition, as a boot drive). You'll definitely see a big change. Not as big as HDD vs SATA SSD, but still very noticeable. It will be way more snappy.
-As @Phaaze88 also said: get a 7200RPM HDD. You'll notice the difference.
Oh, and you can go lower on the CPU wattage if you want to save a few bucks. A quality 550W (or even 500W) PSU would power this build nicely.
Might well be that for streaming the 2700X is the better choice since having more cores. Choice depends on how much you want to do that. I don't do this so have to look at what others say. Might be good to look into that yourself.