There are so many variables that you really have to figure out what works for you. One thing is for sure, you really want to see an ever increasing stockpile as the need for them only goes up. Ignoreing the barracks training size and only looking at orc production, things that need orcs:
- Cater/negotiating
- Fellowship adventures - certain maps/paths
- Workshops - always. The more normal ones you have the more orcs you will need
- Orc troops in training grounds - This can be offset a little by grounds of orc strategists if you have some
- Roads - From constructs (and probably onwards) roads use orcs. Unless you plan to never upgrade I would have a large stockpile of orcs depending on how many roads you have
- Wonders - The new constructs wonders use orcs (and mana/seeds) for building/upgrading. It is possible this trend will continue. So look and see if these wonders might be something you will build.
Things that offset the need for armouries for orcs:
- Orc nests - free orcs
- Grounds of the orc strategist - free troops
- Heroes forge - free orcs
Your number of workshops and the future need for roads and wonders are likely to be the biggest driver of how many you need. I would suggest stockpiling them. You can always adjust up/down as needed as long as you have a stash while you figure out your next plan.
