Don't play a/t as orc.

Orcs are good for one thing and one thing only - absurdly high offense. You need to work with kingdom to make use of that offense, as anything else (including defense) detracts from your shiny elite.

I'd go shep for extra population, and not worry about ambush - you're going to be 'bushed, but the best thing is to overpop someone. you want to assist in chaining, and if plague connects it's much easier to chain effectively. Something like 10 epa, 8dspa, and minimal t/m defenses (you're going to be raped by both).
By doing this the orc is essentially acting as a decoy. Kingdoms will go after the orc first, and after the orc is chained he'll have to cling to life. Fortunately what a chained orc can do is train elites with their credits, keep attacking, and keep suppressing chain victims that can't train up offense or defense nearly as fast. Kind of like how orcs would behave this age, except now you'll have a crappier economy and pretty much have to do so.
Lots of GS help here.

Of course a human can have almost as much offense, better defense, and a better economy all around. And shepherd is immune to plague anyway...