You can easily put similar actions in the same macro. For example the basic 3 GCD combo from each class could be in their own macro each. So for example:

/ac "Dragoon Combo #1" <t>
/ac "Ninja Combo #1" <t>
/ac "Monk Combo #1" <t>

The macro will fire off whatever macro is available as long as there is no wait in between them.