I've got one project where I need to RDP in to a windows server, then RDP from that one in to another one. The second one is constantly unavailable - 'too many terminal services connections' or something like that. But this is only one client, and it'll be over soon. You have my condolences.
admin or console switch depends on version of Windows. One of them will work. Most ppl don't know this. It also has the advantage (in a pinch) that if you need to login to a server, you can log out the current console session and login yourself. Something you can't do with regular terminal sessions (Unless the server is in a domain, and you can connect to terminal services manager remotely and log ppl off)