While I can certainly understand some apprehension surrounding your impending migration from FC to iSCSI/FCoE, there exist almost infinite resources that will provide you with information on making the switch. Considering you'll be using (primarily) VMware, I would suggest starting in the VMware Communities. Here's a great thread (albeit a little dated) that discusses this very topic:
(Don't let the thread title confuse you, the conclusion of the discussion is quite interesting in that the OP decides to stay with iSCSI after receiving feedback about FC from other posters ;-)
There are some excellent posts from end users and VMware support folks on VMTN. I would encourage you to check out the VMTN Storage forums with a few search terms specific to your environment.
Having experience with both FC and iSCSI, I've closely observed the adoption of iSCSI over the last several years and have been pleasantly surprised how quickly iSCSI has evolved into a reliable, robust storage protocol. VMware's support for iSCSI is comprehensive and with vSphere 5, they have released what most consider the gold standard among software iSCSI initiators. This allows for reliably high performance using standard, ethernet network adapters (assuming you'll be employing mainstream, enterprise-caliber NICs in your VMware hosts).
Regarding FCoE: VMware does have some limitations regarding the number of CNAs supported on each host. More information on VMware FCoE Best Practices can be found here:
Here's a great read regarding 8Gb FC vs. 10Gb FCoE. It's a bit technical, but provides some insight into how the technologies differ, and what each has to offer. Understanding these differences will certainly help you to make sound decisions with how you'll configure your ESXi hosts to make the most of your connectivity options.
There are other great articles on the same blog that discuss the some of the topics you've mentioned, I'd suggest poking around a bit, there's some excellent information available there.
Here's a YouTube video from VMware that discusses design considerations for 10Gb and FCoE. It's a bit long, but includes some great advice directly from speakers at VMWorld:
These links should provide some great places to start your research. Feel free to reply to the thread, or reach out to me directly should you have any other questions and we'll be sure to help you find the answers.
Lastly, congratulations on your recent purchase! I offer a sincere "Thank You!" for choosing Nimble Storage!