Some thoughts...
Proxy editing for large files can improve workflow, but they need not be reduced to the very lowest resolution.
A global zoom might best be applied after all other effects/edits are completed and the project saved AS, so as not to overwrite earlier saves.
Open a new blank sequence 2, click the SEQUENCE tab in the bin and import Sequence 1 into Sequence 2. Overlays and audio will not show, but they are there. Sequence 2 is now a single clip of all Seq 1 material. Apply the global effect.
This procedure can also be employed to break a project into clips which can be exported and later assembled. That can be useful for a lengthy effort that becomes unwieldy, and may apply to your second query.
If a direct YouTube upload fails, use their uploader after VP export to an approved YT format.
To lift segments of a master clip, place the clip on the timeline. Split out the desired first segment, then drag it to the bin. A new clip with only that content will be added. Split out another clip and drag it ... and so on. When all the pieces are stored in the bin clear the sequence and assemble the clips onto the blank sequence.