Common Mistakes When Setting up OpenElec on RP
Not setting HDMI options on boot (see last post on CONFIG.TXT) so sometimes no Picture on power up.
Not enabling Remote control of OpenElec so remote apps do not work.
Trying to power off the RP with software. This is not possible.
Using a WiFI Dongle for Video. This can be problematic (interference from Access points, slowdowns caused by range extenders that slow the connection by half, microwave ovens, phones, other RFI) Also the RP has a small CPU and USB devices can offload work to the CPU. It is better to use a main networking setup (like Devolo) or just pay the money and get a fast ethernet setup. Cable and tools are cheap, and switches are really good value. I got a 24 port unit for well under <$150 enough for the house. I used cheaper switches in each room. If you are running cable run 2 cables to each room or 4 or more of you expect more kit. Its good to have a spare cable in case one fails.
Also for HDMI you can run this over long runs with 2 CAT5e cables with an adaptor so add that into your planning plus VOIP and other network devices.
Get a remote most cheap USB media remotes will work fine and you can map the keys if needed..