Hi Benjamin, welcome to planDisney!
It sounds like you're a planner, and that's great because so am I!
Parking Vouchers are valid for 24 months from the date of purchase, so you have plenty of time to use them! Many Guests find comfort in purchasing these in advance, but it certainly is not necessary! My family and I typically just pay for parking on the date of arrival, and we have never had any issues!
But regarding
Genie+, you can start selecting the next available arrival window to enjoy one of the Genie+ Lightning Lane attractions through the
Disneyland Mobile App once you enter one of the theme parks. At the current moment, you cannot do this in advance.
OH! And before I let you go, did you know that you get unlimited
Disney PhotoPass Digital Downloads with the purchase of Genie+? Awesome right? This is a huge perk and make sure to take advantage of this by taking plenty of pictures!
See ya real soon!
Jin