Congratulations !!! The OS is my favorite cabin on non-Oasis class ships. Really nice upgrade !
Yes, you will still get 2X cruise points since your original cabin was already eligible for double points.
You will have 24 hour access to the Suites Lounge and your drinks during Happy Hour will be complimentary. However, no other alcohol or sodas will be complimentary outside of the SL so if you were originally going to purchase the DBP, you probably still want it. Only the Oasis class ships offer 11-11 complimentary beverages.
As you mentioned, there is no suites restaurant on Mariner so there is no complimentary specialty dining EXCEPT for breakfast. You will have access to a specialty restaurant for breakfast (most likely Chops but I'm not sure which one Mariner uses). This is a wonderful perk. It's one of my very favorites. If you want to have specialty restaurant [evening and lunch] dining, you will need to keep your UDP.
Enjoy the OS ! You will be spoiled.