Wow this is a tall request for a NetPro question... I'll try to throw some valid insite into this but no promises. If your new to networking and or uncomfortable with doing this large of an install I would contact a Cisco Partner/Designer. I'm sure your local Cisco Rep can point you in the right direction. I have some names I could send you as well.
On to the question though.
Your requirement for High Avail and VOIP will drive a few things.
1. CORE: Best case would be a pair of Chassis. Deciding what model is another issue. If you plan on just going switching and routing off of it then just use the 4500 series. In order to get you up 12 floors your going to need to use Fiber links so SFF fiber cards and GBICS will be your best bet here and will leave room for expantion. Using redundant 4500's should allow you to use 4506's. If you cant justify dual 4500's the use a single 4507R with Dual Supervisor modules. In either case your redundant links to your edge switches should not come from the same line card. In the case of redundant 4506's thats simple one link to chassis 1 and another to chassis 2. In the case of a 4507R you would need multiple line cards and you would connect link 1 to line card 1 then link 2 to line card 2.
Again redundancy planning and implementation should not be take lightly your companies revenues might depend on this being done right.
2.EDGE: You have a bunch of options here. Based on your end user numbers you could probably go with 2960 POE switches. Cisco has done something interesting with their switch line in this latest offering. That something is that the high end 2960's, the 3560's 3760's and 6509's with Sup32 all use a 32 Gbps backplane. So as far as backplane (port to port communication) goes it is a pretty even playing field. Its when you start looking at features of the different model that you need to be careful in your choices. With VOIP in your plans you need to put lots of thought into what phones you plan on using and what voltages they pull. Based on your requirements for HighAvailability you will want to make sure that you have 4 SFF interfaces on your edge switches. This will allow two ports back to your CORE and at least one more to trunk to another switch in the closet. The trunk to another switch will create a failover path if your fiberlinks to your core are cut or if your CORE goes off line will provide at least switched access for clients on the same LAN/VLAN.
I'm going to cut it off there because this could go on and on. When we do this for clients we usually have multiple planning sessions and both engineering drawings of the facility and Logical drawings of the network to plane the scope and scale of the project.
I will monitor this conversation and will gladly answer any more questions you might have or pass along information you might need.
Good Luck,
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