that looks pretty fantastic for a month of learning. Really nice job showing the volumes.
For brighter/more vibrant, don't worry too much about going too far. Pick a brighter highlight color and layer it on smaller. Use a pinker violet underneath with more contrast. Just try stuff, and when it's too much you can put thin layers over it to draw it back.
In that picture from behind I think the muscle shading looks great, but I'd keep using brighter layers on the flats to bring it up a little higher. I imagine if you check a reference it'll go higher value like that.
Some parts looks like white drybrushing. If you want more saturation there you can glaze on a highlight color just for the hue.
Glaze basically just means using very thinned paint but without much paint on the brush, so it doesn't run like a wash. Setting up a glaze is basically the same as a wash but drain your brush more. You can check the consistency on a fingernail.
You also mentioned wanting smoother blends, which you can also get with glazes, going back and forth between the two colors like a series of micro layers. It helps to keep layers thin in the first place and stipple the edges with texture rather than use hard lines.
For my personal preferences, I think it looks smooth enough already and I'd focus on getting light and color the way you want it. Blending issues you notice in closeup photos disappear at arms length and sometimes making thing smoother makes them look less defined at a distance, so it depends what you're going for.