When connecting to a host multiple times, you can re-use the first connection to speed up subsequent connections. This makes connecting many times faster.
ControlMaster auto ControlPath ~/.ssh/master-%r@%h:%p
It is possible to add port forwarding on the fly without the need to open a new terminal and ssh connection. ssh provides some escape characters to do some stuff in your current connection. In the default setup the basic escape character is ~ (you can specify this by using EscapeChar in your configuration). If you follow this by # character (and thus type ~#) you get a list of all forwarded connections. Using ~C you can open an internal ssh shell that enables you to add and remove local/remote port forwardings.