I switched from counters to the Martian Metals 15mm TFT figures that came out in the late 70s. I've supplemented their figures with other manufactures' figures over the years but have stuck with the 15mm size.
I craft terrain pieces myself. The FB group 'The Tabletop Crafters Guild' is a good resource for sharing tips and inspirational photos. The main hosts there also have YouTube videos to step you through their builds. They mostly seem to use 28-30mm figures but the ideas are the same for any size.
Rich