Would this setup work?

[jdx3ds]

Ok i was thinking of getting an HIS IceQ turbo 6850
a 24" Asus monitor with DVI/HDMI but no Displayport
an old Dell monitor with I believe DVI

and maybe a 2nd Asus monitor in the future...

would it be possible to use Eyefinity in the future?

could I add a second 6850 later on in the future? I am getting a full ATX motherboard with plenty of slots

 

[hang-the-9]

If your motherboard has crossfire support and your power supply is good enough, yes.

 

[jdx3ds]

What would be the min wattage to buy?

 

[gidgiddonihah]

Plug your data into here: http://extreme.outervision.com/psucalculatorlite.jsp.

I always add at least 50-100 watts to the recommended wattage to give me some extra breathing room. I also add a ton of PCI and PCI-e components and the overclock i want to give it with lots of extra voltage. This way it gives you some extra breathing room for upgrades, and I like as much as I can afford. But at minimum hit the recommended it gives you.

 

[hang-the-9]

What would be the min wattage to buy?

6850 has a 500 watt requirement which is usually 20% or more than what you really need, for crossfire, 700 watt god quality power supply will be safe with pretty much any CPU/hard drive setup.
AMD has a list of "certified" power supplies http://support.amd.com/us/certified/power-supplies/Pages/listing.aspx

Not really a full list of what you can pick from, but has more than enough models to choose.