Because of your oxygen, you will be using the
scooter while waiting in line.
In most cases you will be able to keep using it until you actually board the attraction. For many attractions, you will wait in the line with everyone else and just before the 'regular' line reaches the boarding area, guests traveling with wheelchairs or
ECVs are pulled out of line and routed to the exit to board. When you finish, your
ECV will be waiting right there at the exit for you. If in doubt, you can ask the CM at the front of the attraction, but in almost all cases, your ECV will either be with you or right at the exit.
For movies and shows, you will be able to drive the ECV into the theater and stay seated on it for the show.
There are some attractions where a guest traveling with an ECV needs to transfer to a wheelchair that is available at the attraction. You would not be able to push the wheelchair and there are no CMs available to help you push one. If your ECV is small and manouverable enough, you
may be able to continue using it for the attraction; it really depends on the scooter and the attraction. Ask the CM if there is one of those you want to go on.
You can also find an icon on the park maps that will help you - a picture of a person in a wheelchair all by itself means the attraction is wheelchair and ECV accessible. If the little person is getting out of the wheelchair, that means it's accessible but you need to transfer to a ride car. An icon that includes a person getting off of the ECV is one of the attractions where ECV users usually have to switch to a wheelchair.
If you go to the disABILITIES FAQs thread, you will find some information in post # 3 that will help you. Near the top of that post, there are links to the WDW Guidebooks for Guests with Disabilities for each park. They give some very basic information, including how accessible an attraction in. There is also some helpful information, with pictures, in the Epcot FAQs thread, also stuck near the top of this board.