Pretty cool, T! The symmetry weasel reminds me of Madagascar, you know...the animation flick... forgot what creatures they were meant to be...maybe lemurs?
Very funny, though!
When you do portraits, it's probably best to first try working without fluids. It takes a certain kind of clarity and quietness to really stay on top of things with fluids that even I often can't muster up. So...first you want to realize that you know what's happening, know what you want, you know. Then you can begin to consider raising fluidity levels.
Really, the most powerful and useful fluids get in controlled situations is for perfect and painterly smudging/blending. That's where their most excellent traits come out. At that point, then, they're also no longer experimental, but virtuous tools.
Back to your old man, there are some really great choices in him, especially on the sense of the skull beneath him, but there are a number of lighting confusions and the eyes are downright terrifying, hehehehe...which could- on purpose- be considered masterful!
One interesting method I figured out over the years was to really almost mimic what I'd do in 3d. I would make myself a hairless head without any features other than an egg with a chin, so to say, hahaha. I would light it properly with only one light source. Then I would try to carve out and push the features such as nose and eyes and cheeks, already creating drop shadows, too. I would continue until all major features are there. Then I might start putting colors in, very explicit stuff such as red on the cheeks and chin, nose and beneath the eyebrow, maybe, blue on the inside and under they eyes and on the temples, maybe some brightness variations where appropriate, considering sun exposure and so on. I might even go in for the finer details then, like specific textures on skin regions...if I get carried away, hehehe. But the real fun begins when I add a second light source or even a third.
To do that I often stay just on one layer, but just the other day I had great fun with making an additive layer and really just painting pure light on this one. That was fantastic fun and super easy. You can afterwards even play with the light, even change colors by brushing over it with 0 fludiity and 0 build up, if you painted with transparency, of course.
Anyhow... that's one of my techniques for reference free subjects.