First one is easy, just type "*.sldprt *.sldasm *.pdf" without the quotes in the name field.
For the second part you can only search in one workflow at a time under the workflow tab in complete search. However, if you think searching multiple workflows at once is something your organization is going to do often, I would guess you can create a workflow variable and set it in each transition. Then search that workflow variable using the variables tab with or statements. If these searches are consistent, i.e. always/or often searching for files in workflow "X" "Y" & "Z" you can save it as a favorite so that you're not reentering the search every time.
I did not realize you could have multiple extensions in the default container. That'll work great!
I was hoping I didn't have to use flags, but its an easy modification.