Is it possible to Rally a new Guerilla or cube onto the board, and then Launder a Cash token to take an action with that Guerrilla or cube (e.g. March/Terror)?
Also, can I use Rally or Train to put a base on the board, and then use that base to Rally more Guerillas/Police onto the map?
No, a given space can only be selected once per operation. If you are talking about Laundering for an extra operation then Yes.
Finally, can I Launder Cash to get two Civil Actions in one Event card?