Welcome, Daniel!
It sounds like you are quite the Walt Disney World Resort planner. You must have done your research as I can tell from your question you're well-versed in all the planning tools such as
Lightning Lane Multi Pass, Virtual Queues and even
Park Hopping. Well done! As the Jedi would say, The Force is strong with you.
Yes, as long as you don't have theme park admission that still requires a
theme park reservation, Guests can request to join the 7:00 AM attraction
virtual queue even if they plan on visiting another park first. As you stated, if you are able to get a boarding group, you'll need to keep an eye on when your boarding group is called. You'll have one hour from when it's called to get to
Guardians of the Galaxy: Cosmic Rewind. If you aren't able to secure a spot in the 7:00 AM attraction virtual queue, you can try again once you enter EPCOT for the 1:00 PM virtual queue.
Guardians of the Galaxy: Cosmic Rewind is one of my favorite attractions, so if it's in your budget, I highly recommend purchasing the Lightning Lane Single Pass in order to experience it. You can request to join the virtual queues as well, so you may be lucky enough to ride it twice, but with the Lightning Lane Single Pass, you'll have a shorter wait and be able to choose the arrival window that works best for you.
Have a wonderful vacation, Daniel! Please let us know if we can help with anything else.
Magical Wishes,
Lauren