Can AIs manage elements of my company for me?

Solution 1:

At present, AIs are exclusively for competition. This is probably in part because OpenTTD, more so than its progenitors, is a multiplayer game, and giving players access to that kind of automated tools would damage game balance.

There might exist patches that'll let you offload certain aspects onto AIs, but that carries with it its own set of problems (compatibility with trunk saves, for one, and also the fact that quite a few patches appear in one version, remain supported for a few version, and then wither).

Additionally, half the fun of a game like OpenTTD is all the micromanagement. ;)

Side note:

One patch designed to alleviate some micromanagement issues, albeit in a different maner from what you describe, is cargodist, which is well-supported and popular, but the above notes on versions and support still applies.