Hi-- when I bought a metro pass, only available was the 10QR plastic card that is rechargable--and when you buy it the initial amount is 10QR for 5 rides and to top up 10QR amounts is the minimum. You may find that you can do something beyond buying the card. But I didn't see that option. There is a 6QR max for riding in one day. You still have to tap the card to enter and exit but it stops deducting money after 3 rides. If you are in Abu Dhabi or Bahrain in the next 15 days, I will happily pass along my card with the remaining 4 QR on it!
There are loads of people working on the metro to help out. If I so much as looked at my phone for directions, somebody was there offering assistance. And there are workers at the metro entrance and in offices at all the stops I stopped at. Great announcements and signs in the metro, too.
Yes, the Pearl upscale shopping and staying-- I stayed around the souq and Islamic Art museum.
I do think 15 min is enough to walk between the 2 museums--maybe 20 if you are unlucky crossing the street-- the stop lights can last while--crossing the Corniche is brutal----if you don't wanna walk, you can go to Islamic Arts, walk to the Pearl statue, cross the street to the Souq and then take the metro (yellow line) to the National Museum. It is all very close in that area. And I found Doha very walkable-- wide sidewalks with ample jaywalking (except the Corniche)!
I didn't go to any malls-- that leaves me something to see next time!
The library is great-- nice place to sit and read, have a coffee and hang out. The metro (red line) stops right in front of the back of it!