You cannot trigger sequences on the Maestro, but you can use the "Copy all Sequences to Script" button to add a set of subroutines to the end of the current script, where each subroutine represents one of the sequences. You can then send the Maestro serial commands to trigger those subroutines. How many sequences can be stored on the Maestro depends on the size of the sequence. The 12,18, and 24-channel Maestros can each fit a script size of 8KB.
As for your last question, I do not see a problem with controlling multiple Wixels that way, but you would have to write your own program that does that. This post by David features a link to a wireless_serial_channel app, which allows you to change the radio channel at run time to communicate with more than one Wixel. The post also has other apps that you might find useful.