Recently purchased this awesome title on GoG (adored it as a teen) - Which are the best mods to start off with? (is there actually an active modding scene for TA). What is the best source of said mods?

sorry that this doesnt answer the question, but if you really are into modded version you could check SpringRTS (google, i cant post links) which is an actual 3D engine based on TA and now supporting many different mods but also Versions of classical TA with some updates that make it worth playing still today. (Balanced Annihilation for example)