Nice!
Admittedly I think you might have missed the mark with the boot print, partly due to execution (just offering constructive criticism).
That aside... For a first sculpture I think you did a great job.
I have limited sculpting experience, but when I used to sculpt I used epoxy putties (often called "green stuff" or "white stuff", and often sold by specialist hobby miniature stores, or sometimes marketed as plumbing compounds). They have a long curing time, and when mixed they have a relatively tough consistency, while staying pliable for hours, allowing you to spend time perfecting details.
For smoothing I used to coat my fingers in a bit of spit to smooth out the finger-prints, followed by fine-grit sand paper, finished with a rouge cloth... Normally I would prime with an all-purpose spray paint like krylon before painting with acrylic-based paints.
I've never done anything on this scale, and think you did an excellent job sculpting, as far as I'm concerned