i think so! i was able to get rover's briefcase by tt-ing back to the may day event (which took place on a diff island too) so should be possible for this too
Yes, this works. Alternatively, say you have some time next weekend, just hammer out the event until you get all of the items you want. Once you're done with that day's event, time travel back a day and do the event. Then reset it back to the normal time, you can then redo that day's event. You can even time travel towards the end of the events so that you can unlock all of the items to purchase.
yes, you can also travel back and do any of the events so far (easter (unfortunately), may day (you only get one ticket a year though), museum stamp rally, and earth day)