Dawnguard has been released for a day now, is there more than one crossbow?

yep

Infinite amount of crossbows.
2 types
2 subtypes of the 2 types.

*Read at your own risk* Technically there are 2. Steel/normal, and Dwemer. However, there is an enhanced version for each which gives 50% armor penetration. Then there is 2 bolt types, each has 3 different upgrades beyond the normal ones.

how do you get them

Doing quests for the Dwemer obsessed chick.

no idea where she is or who it is

Do the dawnguard quests. You'll run into her fairly early on.

There are four crossbows that can be obtained from doing all the ''Ancient Technology'' quests.
1. Crossbow
2. Enhanced Crossbow
3. Dwarven Crossbow
4. Enhanced Dwarven Crossbow
You can also receive different bolt types by doing the quest.
1. Flame Steel Bolt
2. Frost Steel bolt
3. Shock Steel bolt
4. Dwarven Steel Bolt
I personally use the Enhanced Dwarven crossbow with Fiery soul trap and absorb health on my Archer it does 113 damage

do they hold up to higher tier vanilla bows or no? I want to replace my current ebony bow with a nice steel crossbow.

The best enhanced dwemer crossbow does more damage than a dragonbone bow. However, dragonbone arrows help balance the damage out, but the crossbow does ignore 50% armor.

On top of that, you can technically have shock, fire, and frost damage when using the crossbow, considering you are using an enchanted bolt and have the dual enchantment perk.

Can you upgrade them via smithing? Are they more Damage than daedric bows? I have a legendary daedric bow that does 210 dmg..

Yes crossbows can be improved via smithing. The best crossbow will do more damage than a daedric bow.