To answer your questions:
The hardware requirements for hosting the server should be the same as the regular dedicated servers (I had the exact requirements somewhere but I can't find them right now).
As Paulofonta correctly stated, the client-hosted dedicated server does allocate more RAM in order to actually load the level, however usage after that remains similar to the normal dedicated server. (I haven't seen it grow more than 150MB of usage on initial map load, compared to the 100MB the normal dedicated server uses).
As to whether it's stable, I'm happy to inform you that I've found it to actually be more stable that the normal dedicated server.
There is some functionality still missing, which mostly includes team management (balancing), Conquest flag logic, and RCON, however we are currently working on re-implementing everything.
Speaking of RCON, as I said it's currently missing from the client, but worry not because we are re-implementing, and extending it with our custom commands, so can manage your servers via your favorite administration tool (eg. ProCon) like you normally would.
We might not be able to provide every single command when the Closed Beta launches, however we will make sure that we provide everything you need.
Finally, when it comes to hosting limitations and management, as RobbingHood correctly stated, this is an effort to prevent abusive use of our services.
The limits and the upgrade criteria will be pretty generous, so don't worry about not being able to host the amount of servers you want.