Yes, it is a good approach. However if you need to do something with the result of the first call before making the second call, (such as extracting the args for the next call), then you might run into trouble since the command won't hear any notifications coming back from the Proxy, and should not place listeners on the Proxy's service.
Another good approach that takes care of this (and doesn't require AsyncCommand) is the ServiceRequest pattern, which I describe in the O'Reilly book 
Essentially, a normal Command can send a formal request (based on Observer, and containing a callback to the command) to a Proxy method. The Proxy hangs onto the request (keeping the Command in memory since it has a reference). When the service returns, the Proxy sends the data back to the caller (the Command), which can then make the next request. You could make all your calls from the same SimpleCommand OR you could have a MacroCommand with three SimpleCommands that all do this. The first subcommand could set the results in the body of the note for the second subcommand to use and so on.
Although I think you'd find the explanation in the book more complete, here are some links to the relevant code:
The ServiceRequest class:http://examples.oreilly.com/0636920022459/StoryArchitect/src/com/futurescale/sa/controller/command/story/SearchStoryCommand.as
A Command that creates the request:http://examples.oreilly.com/0636920022459/StoryArchitect/src/com/futurescale/sa/controller/command/story/SearchStoryCommand.as
A Proxy that handles the request:http://examples.oreilly.com/0636920022459/StoryArchitectModel/src/com/futurescale/sa/model/proxy/StoryReadingProxy.as
Also, this formal request pattern works for any async operation, and the application in the book also makes use of it to allow commands to request a popup and get called back with whatever the user's choices/input were. This makes it a really useful pattern.
Just for fun, here's the popup subsystem. Notice how the AbstractPopupMediator handles the request and the subclasses just have to basically return a different popup component and be interested in a particular notification:http://examples.oreilly.com/0636920022459/StoryArchitect/src/com/futurescale/sa/view/popup/
ActionScript Developer's Guide to PureMVC http://oreil.ly/puremvc