First disclaimer: I am NOT an expert - so what I'm about to say is just what has worked for me. This is also restating some of what has been said before - just with few more words.
Also - listened to the first vid, watched the second. It does sound to me in the "Thriller" vox like MJ is possibly moving back from the mic a little during the louder parts. Just something about the sound seems a little more "distant" to me in those moments. That all being said...here's how I would break down your problem:
- The level of the mix (you want this where you want it, for comfort)
- The level of your RECORDED vox (you want this to not be clipping, and to have whatever quality you want the unison preamp to be imparting)
- The level of your vox in the mix, so that you can hear yourself no matter how you're singing.
So - let's attack those one at a time:
1. Level of the mix. This one is easy. Set it where you want it.
2. Level of the RECORDED vox. This is more subjective. Generally I think you would want to set this based on your loudest vocals so that it has the color (and doesn't have the clipping) that you want. This means that there will be a lot of dynamic range in what you record (unless you print compression). That's because your softest notes will not drive the preamp the way your loudest notes will. But they will still be recorded - and you will adjust dynamics for the soft parts as you mix (later in the process).
If you want your softest notes to drive the pre-amp, then you'll need to record them separately (so that you can turn the gain up). This is would be totally normal to do.
OR (not sure if this is correct) you could apply compression on the way in, to level your signal across the dynamic range. Or maybe you could use something like the Manley Voxbox (which has compression integrated) instead of the Neve 1084 (which doesn't). There was a good UA video on using the Manley Voxbox to record hip hop vox which showed a bit about how to do this.
You definitely want a pop filter so you can get close to that mic without causing plosive problems.
3. Level of your vox in the mix. You have some options here. In terms of the dynamic range of your voice, I would probably opt to apply compression on your vocal to what you're monitoring (i.e. not to what you're recording - you can choose). You probably already know this, so forgive the oversimplification, but compression will allow you to boost your overall signal (i.e. bring up the volume of the soft passages), but will keep your loud passages from blasting you (because they're being compressed). So the effect in your headphone/monitor mix is that your soft passages will still be loud relative to the mix, and your loud passages will be compressed. Whatever effects compressing the loud vocals creates, as long as it's ok for you to hear, won't be printed to the recording. You do also have a fader where you are controlling the level of your send to the monitor mix (without affecting the input gain that you're recording). After you get the input gain where you want it (step 2), then you just need to do some experimenting with the compressor and the fader that sends to the monitors, and you'll probably find something that feels good in your ears with some experimentation. Plus having a pop filter will let you work the mic, especially if you lean in for the soft passages.
Hope that's helpful! That's what's working for me so far. I'm learning as I go.