Finally everything turned up. A few modifications were made along the way due to stock availability and other issues. The total price went up from around £2600 to £2800 by the time various changes had been made. The kit list linked in the previous post has all of the amendments on it, and is actually the final item list as it stands now. The kit I ordered in the end was specific to the rough design I had in mind...
The design of the environment wasn't set in stone. I had a vague idea of what I wanted to achieve...
Network Attached Storage
I decided upon building a NAS server using XPEnology, a rebuild of the open source Synology DiskStation OS. This would let me build a system that thought it was a Synology DS3612xs (a unit which runs at about £1800+ without disks) but with a bit more flexibility. XPEnology DSM 5.0 however doesn't support some of the features that a real Synology system does, specifically SSD Caching and the ability to present block level iSCSI LUNs. My system would run DSM-5.0 4493 Update 1 with 4 x 3TB disks and 5 x 1Gbps NICs. I would use it to present file level iSCSI devices to my ESXi hosts, and also use it as a Plex Media Server for home entertainment.
ESXi 5.5 Servers
I would build a pair of ESXi 5.5 servers. I opted for motherboards which had 8 DIMM slots that allowed me to utilise 64GB memory kits without the added expense of using ECC RAM. However, the CPU support list for the chosen motherboards (MSI X79A-GD45 Plus) was fairly restrictive. The board supports LGA2011 socket processors, and the cheapest compatible CPU I could find was the Intel Xeon E5-2603v2 (1.8GHz, quad core, 80W TDP). As I'd already purchased a pair of Plextor 128GB SSDs which I hoped to be able to use in the NAS (but couldn't), I decided I would repurpose them as Virtual Flash in each of the ESXi hosts.
The old 8-port Netgear desktop gigabit switch just wasn't going to cut it any more. As all three of my new hosts had 5 NICs each I needed more switch capacity. Originally I ordered a Linksys SWR2024 24-port Gigabit Managed switch from eBay, but after having some issues with the seller I asked him to send me a refund and I ordered a Dell PowerConnect 5224 instead. As it happens, the Linksys got shipped before the seller got my request for a refund, but because of all the inconvenience he decided to give me a full refund too and let me keep the Linksys switch, which was nice.
The Dell PowerConnect 5224 arrived first and so that was the switch I went with in the end, and I'm glad I did. While feature wise the two devices aren't too disimilar, the Linksys is a lot noisier and can only be properly managed through it's ancient web GUI which required Internet Explorer 7 to work properly, which mean I'd need to keep a Windows XP VM on hand just to manage it.
I've been blown away by how cool this thing is. I bought the Pi with the intention of using it to do just the remote power control (e.g. Wake On LAN), but after having got my hands on it and realising it's potential it's now doing a LOT more stuff for me. Best £30 I ever spent.