Need guidance with a datapack that seems easy on the surface.

I'm trying to make a datapack that executes a command under certain conditions. The command is responsible for spawning a mob but it's from a mod and not the default summon command. The conditions I'm trying to achieve is to run this command in a random proximity from the player when at certain locations (for example at a biome or at a structure) to sort of mimic natural spawning. I'd really appreciate some tips on what aspects do I need to learn to get such results. Currently image attached is what I managed to do lol