I use a third-party monitoring service to monitor the Dir and OR ports of all my relays. It's especially useful now that Tor Weather isn't maintained. The service constantly checks for a response from both ports, using several monitoring endpoints around the world, and notifies me of any downtime. It also has a nice feature where I can look for a specific response from the Dir port (i.e, parse
http://relay1.example.com/tor/server/authority and look for the fingerprint).
I don't know of an easy way to aggregate the Tor stats in one place, but over time I've realized those stats don't matter too much anyway. :) As long as the nodes are running well and providing service I don't really need to know how many circuits or the bandwidth at any given moment.