Aren't 1-3 baked into the OS?

1. Just add multiple Google accounts in Settings -> Mail, COntacts, Calendars
1a. Log into your TripIt account and find the webcal link for your calendar feed, then add it in iOS (Add Account -> Other -> Add Subscribed Calendar).
2. This is how iOS works.
3. It just works. What are you not seeing?
4. The stock Calendar app will only ever use Apple Maps. I use Week Cal, which pops up a little window asking which map app you want to open things in.