I've been Digging Deeper several times now, and wow...
My first two fort were lost to raptors (Yeah, I'm a masochist). After I gen a new words without them, I started feeling the orc challenge. My third fort was lost to a goblin ambush (They showed up just after the orc and killed my two remaining crippled dwarves. :p
For my fourth fort, I built a looooooong hallway full of stone-fall trap for defence. (Yeah, next time I'll read the raw before playing).
For my fifth fort, I decided to lock myself in the mountain. First siege went away, but while I was stockpiling some wood, a second siege came. I don't know why, but every single dwarf in my fortress decided that he didn't want to pull that lever. I drafted them all, and hid them in the bedrooms underground, hoping to dig an escape tunnel and send a dwarf on a suicide mission to lock the orc inside the fortress. Well, none of them had a pick, so my plan was an epic fail. I spend a nice moment looking the Orc Axelord picklocking the bedroom's door one by one and imagining the face of the dwarves hearing the screams of pain nearer and nearer and then the unique noise of somebody picking a lock... their lock!! :p
As for my sixth fort, I decided to fight back. I immediately started training 3 dwarves as Hammerdwarves while my smith was churning out steel armor and weapons. I crushed the first siege losing only one dwarf and two dogs. (I could have fared better, but my marksdwarf decided that he absolutely needed to patrol the hallway 2 z-level under the battlfield).
Then during the next seasons, while all my dwarves were undrafted to help clen the mess, 3 squad showed up and killed them all. I couldn't help but think of the world "gangbang" when watching 15 Orcs hacking at my last, unconscious dwarf.
(For unknown reasons, my orcs were labelled as active for all seasons)
On an interesting sidenote, I'm no playing as an adventurer. And since I stopped creation in 25 to keep the megabeast alive, there is currently more failed Mountain Hall than active settlements on the world map. :p
Anyway, good job! However, If I could add a few suggestion....
First, definitely add the Building destroyer tag to the orcs. Even if it's not useful, having an horde of Orc pillager wreacking havoc in your fortress is just more realistic.
Second, if you plan to do some more work on the plants, could you please make a total conversion to real ones? I enjoy having my dwarves eating potatoes and oranges, but "Longland grass" jsut don't fit in. :/
Third, I don't know if you can do something about it, but since I installed your mod, I never get any migrant on the first two years (And sometimes even later). And fighting 45 Orcs with 7 dwarves is just not possible.