W-O-W!!!… Out-freaking-standing! Gorgeous figures, terrain, and tabletop…
About using epoxy to attach your figures to their MDF bases. I mount Army Men, made of Low Density Polyethylene (LDPE) plastic, to 50mm MDF square bases, using Multi-Temperature Hot Glue. They stay stuck, very solidly; it is difficult to remove them once the Hot Glue hardens. I, too, texture their bases, using Wood PVA Glue, applying colored mixtures of sand, and Model RR Ballast (small stones). This has served me well, handling the Army Men by the figures, more so than their bases. They get man-handled quite a bit, to be honest. It is exceptionally rare for one to come off of its base, once Hot Glued.
Get yourself a Multi-Temperature Hot Glue Gun. The Low temperature setting issues the Glue in a more viscous state, which has a 10-15 second work time; the High Temperature setting (Glue) comes out very much more fluid -- runs, with a work time in excess of 40 seconds -- too fluid, too hot, too molten, for too long, IMO. Any brand Hot Glue will work, so buy the least expensive brand you can find.
I have had occasions where I needed to rebase multiple LDPE figures (Army Men, Skeletons, Cave Men, and Viking figures, all LDPE plastic, mounted with Hot Glue), removing them from their MDF bases. It was surprisingly difficult to remove them, without damaging their molded bases (several were, in fact, damaged, in spite of my efforts to avoid it). If you need to de-base them, I recommend using an X-actor knife to cut the Hot Glue from the MDF, then flex and peel the Hot Glue off of the molded LDPE base, carefully.
Hot Glue takes acrylic paints, very well, though two coats is best. It can be removed easily, when molten (CAREFUL -- It's Hot!). Once it hardens, it can be cut off, to remove excess; the hot Gun's nozzle tip can easily sculpt hardened Glue, if necessary -- hardened Glue can be sculpted with the Gun's tip, to create miniatures made out of Hot Glue… It is easy to work with, and it is surprisingly effective, and strong, for bonding LDPE figures to MDF bases; the bond does not weaken even after 10+ years. Cheers!