Afaik it works as follows: in the Main Event ticket phase , you can win a ticket you can use for the UOS main event.
You can play as many phase 1s as you like, UNTIL you get a stack through (because only biggest stack counts, they don't combine). You then play phase 2 on a later date and top50 (or more if GTD is exceeded) get a ticket.
As for your 5 major ticket, I don't think you can use it in the phase no.