The first two metrics to look at are CPU and RAM because they are the easy ones.
With 4GB of RAM and 2 vCPU per desktop you're looking at 1.2TB of RAM. Since we get about 8 vCPUs/physical core on average with VDI you can assume you will need ~75 cores to handle this workload.
With dual socket 8 core CPUs (16 cores/server) you would need 5 hosts to handle the load with a 6th for failover. With those CPU numbers you would then need ~256GB of memory per host to handle the load plus one server for redundancy.
So basically:
2x8 core CPUs
256GB RAM
As for storage, if you're looking at standard office/task workers and not power users 100 IOPS will be overkill, unless you have an app that is going to drive that. 30,000 IOPS is going to cost quite a lot. 
I would recommend taking a look at this guide for general sizing but specifically the section on page 7 about storage sizing:
http://www.vmware.com/files/pdf/view/Server-Storage-Sizing-Guide-Windows-7-TN.pdf
20 IOPS per desktop is likely a good starting point. This will put you at 6,000 IOPS instead of 30,000 which will cost a lot less. For added room for bootups/peaking you could go as high as 8,000-10,000. You can take those numbers back to your storage vendor and get some pricing based on those numbers.
Hopefully this is helpful.
-Mike