Clarifications: Octopus card to Kowloon and Airport Express Travel Pass

Hi, i have 2 questions

1.)If I use Octopus card to board Airport Express to Kowloon, they won't accept it as proof to ride the Free Airport Express shuttle bus to Metropark Hotel? But if I show my airline boarding ticket will they definitely let me ride? this is crucial because if I make a mistake it's a long walk to Yau Ma Tei, or long round back to Lai King and change to TWL to YMT, or costly taxi ride :( also, i'm hesitant to ride buses especially arriving at 9PM-ish and not familiar with the city.

2.) I will be in HKG for 5 days. If I buy the Airport Express Travel Pass (HK$300) that has 2 airport express trips and 3 days unlimited MTR, does it also mean I have to use the return trip to the airport within that 3 days? It's not advisable for stays more than 3 days?

Thanks a lot for your time and hard work!