I really don't understand how people are having a problem doing garrisons on alts. I have 5 level 3 garrisons and a few level 1-2's. It literally takes me no time to log them on and set up a full set of missions. If you have level 3 buildings and you max out work orders you only have to replenish those every couple of days. And with one of the garrison addons (I forget the name) you click 1 button to clear out all finished missions and takes a minute to set up the next batch. Set up 6-10 hour missions and then log on once a day, clear finished missions and start a new set of 6-10 hour ones. Every couple of days spend the extra few minutes filling up work orders.
Unless ore and/or herbs are selling really well on your server (which I doubt) then don't bother with the mine or garden. It's pointless.