Chiming in about the tickets not being on your account when you sign in but only showing on the app: DL's accounts & app are much less sophisticated and cohesive than MDE for WDW but they have come a long way in the last year with the app now being able to show tickets on there!
I haven't bought MaxPass yet but I have used my phone to redeem FPs we have pulled with our passes & I always like using my phone better & not having to rummage for my passes in my wallet, but I also have a very large screen (iPhone 6plus) so maybe that makes it easier for the scanners? Not sure, but I have always had them work very fast and once one FP is pulled up, I can just swipe to the side to get to the next persons's FP.
Also, once you do have the tickets scanned at the entry gate & if you choose to purchase MaxPass you'll be able to create a FP party (both of you will have to purchase MaxPass for this). But once you've created a FP party you'll be able to book FPs for everyone in the party at the same time. Also, you are totally able to have your friend create an account & link both tickets with MaxPass in hers as well so either of you can make FP selections for you both and so that you both have a way to gain access into the park too. My husband & I both have each other's & our kids' Annual passes linked in our accounts so either of us can get them into the park if we separate and one parent has the Annual passes.
The only thing you will absolutely need your ticket for is if you choose not to buy MaxPass, you will need the ticket to pull FPs from the kiosks. As mentioned previously though, you are able to use the paper ticket for everything including entry & FP redemption & they hold up quite well for your park days. One tip I have had friends do is to put the paper ticket in between two PhotoPass cards or any other more durable plastic cards such as credit cards, gift cards, etc.