Ryzen processor cores clock down extremely low when idle, and can shift power states in 1ms, so it's not uncommon to see temperature swings of 10-15*C under idle conditions even with liquid cooling, which depending on your fan speed curve could cause fan swings of hundreds of RPM. Depending on ambient room temperature, upper 30s to mid 40s is pretty normal since if you use Ryzen Master to monitor the core load levels, web browsing will show them all rising and falling pretty regularly, like below, which again is normal because of the fast power switching and low clocking capabilities.
As for voltage, AMD's really aggressive with voltage and state 1.5v over short bursts is fine with 1.4s being fine for extended periods, but there's nothing wrong with using a lower voltage, but it will hinder the Turbo capability.
As for power plan, Balanced is what you should be using, AMD collaborated with Microsoft and rolled in Ryzen Balanced's optimizations into Windows Balanced back in...1803 or 1808 I believe, so for all intents and purposes the Ryzen power plans are redundant.
If you want to optimize your processor, and are comfortable "overclocking", fiddle around in BIOS with the multiplier and CPU voltage, start with the highest Turbo frequency and 1.45v, hit it with AIDA64's FPU stress test for about 5 minutes, then start working down the voltage and then multiplier, charting out where stability falls off for each speed, and pick the optimal one. For my 3700X, it was 4300mhz (43x100) at 1.2v. I "lost" 100mhz max turbo, which it never hit anyway, and gained a much higher all core clock with a much, much lower voltage (1.2v vs 1.45v).
It does cap the voltage to what you set it at, but like I said since higher Turbo frequencies depend on (excessive) voltage, you'll lose some low core count higher end turbo speed.
It doesn't matter if you use Balanced or Ryzen Balanced, both are the same.
I've never trusted any software to modify the CPU speed and voltage properly, but I've been doing it since overclocking meant physically flipping switches on the jumper box. While Ryzen Master is a lot more advanced software tool, it's still best to set the final values in BIOS, but you can use them to test with.
As for AIDA64, it's simple to use, and you'll run the Cache benchmark, not FPU. Cache is used to test stability, FPU is for the cooling system.
Just make sure your pump is right side up before you install it, unlike me 
I wanted to give this to you as a point of reference:
3700X 4300mhz (43x100) 1.2000v
Corsair H115i drawing external air
Arctic MX-4 TIM
Ambient temperature 75*F (24*C)
AIDA64 FPU stress (high heat generation), sustained temperature 77.5*C
Yes I'm using a lot lower voltage and have 4 fewer cores...But what does Ryzen Master say your PPT is?
This is what mine looked like for the majority of the test Stress FDU. There was one spike, but then everything settled down and it stayed constant at these values.
