Ok,
I get the impression that you want to build a PC to act as a server rather than building a server with server grade parts.
Ditch the i3-2100 and go for a i3-2120T if you want an i3. RRP is only 10USD more and it supports all the features of the i3-2100, runs a bit slower (2.6GHz compared to 3.1GHz) but uses 30W less (35W vs 65W for the 2100). It seems to be sitting in a sweet spot for the i3 range at the moment.
If you want to go more server than the H61 board (although at more cost), take a look at the newly released Intel S1200KP server mITX board (C206 chipset). Handles ECC memory, E3 Xeon/i3 and Dual Core Pentiums (G620 etc). It has Intel dual Lan and give or take VAT should be around 125 quid. Put a low end E3 Xeon (E3-1225 should be around 150 quid give or take VAT but 95W) or the i3-2120T in it and 4GB ECC ram (both E3 and i3 can support ECC ram). That would take you from the pc acting like a server to a entry level server.
Put the setup in a Fractal R2 array or Lian-Li PC-Q25 case for storage capacity. Add a low rated (400W or there abouts) 80 bronze or better PSU.
Multiuser environments are quite heavily restricted by IOPS of the drives. For home this is not much of an issue but if you start getting large numbers on then desktop drives may start to struggle. SSDs are great for IOPS but are expensive in larger capacities. Enterprise drives are built for reliability, 24*7 duty cycles and decent IOPS. If you can get some SFF drives (2.5") then they will also be fairly good for power usage. Second user drives from companies scrapping old servers may do you if you search around.
The dual networking will allow you to play with redundancy, routing or network teaming (link aggregation).
I am building a clients machine based on this board next week sometime and will put a build log up.
Motherboards tech specs
here (pdf)
If you believe the power of this is too much for a home server then load ESXi virtulization software on it and then install WHS 2011 as a VM leaving you to allocate the underutilized remaining resources to other servers you may want to run. The board and processors support VT-d so if you add a second controller for the drives (grab a M1015 from that auction site for a great SAS2/SATA PCIe 2.0 controller for around 100 quid) you can pass it straight through to the WHS VM for direct control. I do this with my own home server although I use a different board and processor as these were not available at the time of my build. Doing it again, I would almost certainly go down this route.
WHS 2011 will take care for the software side for you as it is based on Windows Server 2008r2. It has an inbuilt webserver (used for its remote access site) and it also has the DNS/DHCP roles available (although unsupported) if you activate them
Downside are more cost, bit of searching around for the parts.
Upsides, great project, especially if you incorporate ESXi (free home use licenses are available) great server with lots of upgrade potential. You'll have to confirm pricing in the UK as I am just basing on pricing I do my builds for over here.
RB