Posting to watch
Assuming you kept all the "good" races in, the main thing to remember starting up is that you have about ~5 seasons to prepare for mithril-armed elves, and about 2 years to prepare for sieges from humans and dwarves. Dwarves in particular are deadly of course.
Year 1.
* Scribe takes the role of both bookkeeper and manager, but needs a nicer office.
* Draft all your Uruks into the melee squad. You'll need cannon fodder too, unskilled orcs or war animals.
* Tribal Craftsman can get you some pretty decent gear fast from leather, bone, ash, & blood barrels. Lamellar robe and Handcrafted Claws or Spear is a good start. You'll probably not be able to mass produce though so also get a regular forge in for some silver clubs, iron spears or scimitars, and shields.
Year 2.
* Win battle with elves in spring. If you're not totally geared up you'll take losses but don't panic, I've seen Orc wrestlers beat a squad of bladedancers to death with their own tiaras.
* Start preparing for Humans and Dwarves. They both siege, so you probably want a
strong ranged squad more dakka. Use the Fletcher's composite bows or if the elves brought you Great bows.
* Build a Slag pit furnace & put an armor stockpile set to "Unusable" only. They'll stack up all the small mithril stuff the elves brought you. Have the slag pit "reforge as crude breastplate" etc. to re-size it.
Random tips
* You won't have common domestic animals, so Drowspiders or Frill lizards to hunt vermin.
* Orcs butcher everything, so plan for a big leather & bone industry. Including lamellar leather and bloodsteel if you feel like the extra steps.
* If you strike mithril or wolfram, get the Damasc furnace, make katanas, mauls, polehammers.
* You can Sell stuff (large gems, cloth, etc.) to get Bayonetted pistols and ammo from the Freelancer's guild.
* If you want to do above ground constructions get the Factory ASAP.
* If you do batch iron smelting at the Slag pit you'll end up with some rusty iron too. This makes fine barbed wire (factory), bodkin arrows (fletcher). Or just use the crucible to clean it up.
* Turn on some "evil races" in the Creatures tab of Masterwork GUI if you want extra allies.
* Get a Stone Circle, craft some instruments. The Orcish music is really powerful, the orc can haste or give combat bonus to nearby allies for 1 month. Not exactly WAAAGH! banners but about the same idea