Welcome to the Strelets Forum. Please feel free to discuss any aspect of 1/72 scale plastic figures, not simply Strelets. If you have any questions about our products then we will answer them here.
I glue a strip of matchbook cover (thin, sturdy cardboard) to the base, more to the side that the horse is leaning to. That usually stops him from toppling over when the rider is applied, as well as causes him to lean back towards a straight position.
Not pretty alone, but when charging en masse you can't tell.
I use a variety of small tools from Sprue Cutters to Diagonal Nippers. For me, the Strelets Horses are simple as I use an ordinary Hand Snipper to remove them from the sprue then remove the stump with a Flush End Cutter. I then use a wide bladed Exacto to even out any bumps.
Finally to smoothe out the base, I simply rub the figure along the bottom of my large wooden desk, it actually works great.