You might want to upgrade to 2020.2 (HDRP 10) btw, you’ll get the “New Scene > Basic Outdoor” scene template. It will already put you in the right ballpark, to begin with, with a PBS Sky, the sun at 130.000 lux, and a rough exposure range, so that you won’t have to create these volumes manually and figure out which sun intensity to use.
Also, I would really advise you to look at this table, as already mentioned above, from the documentation:
It’s nice to see you are experimenting with directional light/exposure in these 2 videos, but you seem to want to make your life much harder by not using physically-based values, It really doesn’t have to be so complicated. 
Also, trying to expose for bright grey materials is not really representative of a common scene with much darker albedo. Point a camera in real life or in many game engines at a bright gray plane in full sunlight, and you’ll often get odd results if you don’t apply some compensation or clamp the exposure manually (that’s why the limit min/max exposure settings are so important).
For instance, in your first video, you’re using an incredibly low exposure (-8.81) for no reason I can think of. That’s the kind of exposure you need to create this kind of scene below (e.g. transforming a night scene into a day-light-looking one). If you look at the table above, -2 EV already is sufficient for a dark night. So, with -8.81, you’ll make your entire scene overexposed (white) during daylight, and then I see you need to reduce the sun intensity as a result and doing some odd things to the indirect lighting. Are you really sure you watched this explanation about exposure and light intensities later in the video?
If you want to use the physically-based sky, stick to 130.000 lux for the sun and leave it there, as indicated in the table above. Otherwise, you’ll just be constantly altering the way the sky reacts to the sunlight, and indeed you’ll be fighting against yourself and have to constantly input odd exposures. And in HDRP 10, using “New Scene > Basic Outdoor” will do all of this for you automatically.
One thing though: if you want to make a time of day (something HDRP doesn’t support out of the box), you’ll need to blend between volumes to handle the exposure nicely for different time of days, OR you’ll need to use the curve mapping mode for the exposure (but that’s quite advanced, I wouldn’t touch it if I didn’t understand how exposure work). Often in games with a dynamic time of day, there will be several fixed time slots/presets for the lighting/exposure/indirect, and as time passes, they will be blended between each other. That’s very roughly how games like GTA5/RDR2/Horizon handle time of day for instance.
So again, please don’t input totally random values and expect the system to work perfectly. 
You can still have a much lower sun intensity if you want, and you’ll then have a tiny exposure range that might be easier for you to control if you have difficulty understanding how exposure works or if you simply don’t want to have such a large exposure range for gameplay reasons for example (a big range is not always recommended for certain types of game where visibility is super important, like Overwatch/Valorant for instance).
