Hi,
Telling you a response, it's difficult. I've been working with VMware for years and design is one of those themes that always have something new to say.
You don't seem to have a very complicated enviroment, but, giving you an advise with this information is more a "guessing" excersise than a proper design.
With that beeing said 
here are some tips:
- Visit this link. For me is a bible and I'm sure it will help you
http://pubs.vmware.com/vsphere-51/index.jsp
- Have a look into this evaluation guide
https://www.vmware.com/files/pdf/products/vsphere/VMware-vSphere-Evaluation-Guide-1.pdf
Do you have any suggestions for a server or components?
Yes. If virtualizing everything, have into account that if you use only one server, you will have a single point of failure. If you plan to use 2 physical servers, maybe VSA could be a good solution for you in order to save money. Use vendor machines that give you support and a "real" warranty.
How many GB of RAM should I use? Is 16 enough for the future?
It depends...what do you have planned for the future? As a thumb guide, summ all the RAM you have now, think about things you will need (for instance if you want to use VSA, you will need to count the RAM the VSA appliances will use in every host) and add 20%. Yes, with this configuration you are not achiving the best price as you are not considering overcommit benefit of RAM. But, without having a nice understanding of your "normal" RAM use, this would be the best approach I think...
The same question about HD capactiy? 5x 3 TB HDDs in a RAID 5 configuration? (12TB)
I'm not a big fan of having SATA disks for virtualized enviroments. More important than size is performance and those drives have the worst performance in the market right now. Consider SAS drives with at least 10K RPM and 450-600 GB each. Just today I have a session in VMworld that explained lots of details about designing a storage...it's impossible to simplify it in few words. But think in terms of "redundancy" (RAID 5 only gives you 1 single point of failure), "performance" (IOs and latency) and in the last place, "capacity"...I say the last place because it usually is the easiest thing to calculate. With VMFS5, Volume maximum is 64TB (file size maximum is 2TB -512 bytes)...but you can always use RDMs with physical compatibility to overcome this.
Which CPU? Intel Xeon?
Intel or AMD are ok. 64ibts is necessary and hardware virtualization is a reaaaally good thing. The more cores, the better
Do I need a graphic card?
Yes.
Anyway, THE BEST ADVICE I COULD GIVE YOU, is that you get in touch with a vmware certified partner to help you. It will cost you money? Yes. But, how important is the information you are going to virtualize? Be sure that you don't run into trouble having a solid solution, well installed and monitored with a proven and tested backup solution.
Regards,
elgreco81
