Welcome to Librarium Online!
I can't tell you why, but after a week of thinking about it, I have chosen Orcs & Goblin. But the thing is, I want an all-mounted army. As in, every single single model mounted.
First of all, is such a thing possible under the rules?
Is it viable as an army? Even if it's not, i'll still play it, because I think it's so cool.
Also, are spider riders as cool as I think they are?
Well, let me first say that you are taking an interesting approach - Orcs and Goblins normally aren't known for their cavalry. not a bad approach by any means though - it will definitely be interesting for you to play something different.
As for whether it is possible under the rules - it most certainly is. All of your unnamed lords and heroes can ride something - all orcs have access to boars, boar chariots and wyvern (Warboss and Great Shaman only), and goblins can ride on a wolf, wolf chariot, gigantic spider or giant cave squig (Night Goblins only). For core units you've got access to goblin wolf riders and forest goblin spider riders. For special units you have an absolute heap of options - orc boar boyz (savage or otherwise), orc boar chariots, night goblin squig hoppers and goblin wolf chariots. Finally, you've even got the snotling pump wagon to round it all off in the rare slot!
As for its viability - I can't honestly say that I know. I guess I'll leave that for you to find out for me! I can say however that spider riders are pretty cool in my opinion. They look great and on scenery-heavy boards are about as maneuverable as you can be without wings.
Hope this helps,
Its actually quite a fun option, I have run an army list that was full of wolf boyz, boar boyz and gobbo chariots and it seems to freak people out. The charge range of the wolf chariots is brilliant and you can use the wolf units as fast cavalry to pull the enemy around. Using things like boar boyz or savage orc boar boyz as your big hitters does a lot of damage as well.
Helper monkey, bring me beer and donuts
Also you can mount gobbos on giant squigs and use squig hoppers can't you?
Gobbo big bosses on qiant squigs give me a case of the shivering fidgets, I just get paranoid about them!
edit: sorry just noticed this was covered, my bad.
aut viam inveniam aut faciam / I'll either find a way or make one.