My take on Steam: it works just as well as the disk version (one minor quirk I know of, more later) provided you keep the
virtual store issue in mind, as you do for the disk installation, and apply the
rename guide if you want to play older mods ("kingdoms.exe not found" will be your clue).
Admin\compatibility solves a number of issues, especially graphic related ones.
As to the quirk: that's a modder issue - steam does not generate new string.bin files for data\text\battle, strat, shared and tooltips. Which means a modder will have to provide the updated string.bin and cannot just provide updated txt files as is the usual practice.