You have to wait till you check in since your room is separate from your UPH. There is a Disney desk at both the Swan and the Dolphin where you can purchase your tickets. If you just want a regular park hopper you can get that anywhere, but the UPH requires onsite stay. Our room wasn't ready when we went the end of June, but we were still able to get our passes very easily upon verifying that we were staying at the Swan. Yes, you can take off the first and last day of your park hopper with no trouble what-so-ever!
Hope this helps!
Debbie