When you say "webhosting a few relays" I think you mean "webhosting on a
few servers". You do not need to run a Tor relay in order to host a
hidden service.

You won't be able to access all the hidded services at the same time if
you copy the same hidden service key to multiple hosts. However your
overall approach is what the OnionBalance tool implements
(http://onionbalance.readthedocs.org/).

With OnionBalance you can host a hidden service on multiple servers, and
clients will be directed to one of the online servers. It is basically
'round-robin DNS' implemented on the Tor hidden service protocol.

Let me know if you have any questions!

Regards,
Donncha