As for painting faster, I’m in the same boat as you. I could have gone a bit quicker, but even when the best ideas strike, actually getting on with it makes a world of difference. Instead of starting to paint straight away, it’s often an evening project now, which isn’t so bad because there’s more light, but then I do end up feeling tired after a day of working, rushing about and running up and down.
I’ve cancelled all my painting lessons outside the home for the coming week, but I’ll see if I can do some preparatory work whilst out and about and at work.

I think your style of painting lends itself perfectly to painting several sheets of paper in a row or one below the other. This might well be the best option. I did it once with cats. You could then complete these in a day, sell them, and, if there’s time left over, do the basic sketches for the next day’s paintings, and perhaps touch up a few bits here and there the following day.
In that respect, creativity knows no bounds.
I hope it doesn’t cause you any stress.
Have lots of fun, and good luck with the sale.