dont do stuff cause it will make your application better, do stuff cause you enjoy it and it lies with your interest which you can conveniently talk about in your personal statement, all this stuff your doing will be talked about in a 4000 CHARACTER statement so you dont have alot of room to talk about everything. i did alot and didnt get to talk about all of, chose 1 or 2 big projects like volunteer work or the paper and debate thing sounds fine (but not at the same time cause doing so much at alevel might burn you out) but remember its not about what you do its about what your learnt, how did it develop characteristics, how will it help you with your course or aspiring career. dont overdo it you maybe eager now but alevels take up alot of your time so just try one thing at a time dont over work yourself, burn out can be a big problem at sixth form if you dont manage your time appropriately
from personal experience
NCS: yes, i enjoyed it, i went with 3 friends and made 3 more, the activities were fun and i talked about it in my personal statement
DofE: i havent done the expedition yet but if you plan to do volunteer work do it while ur doing DofE cause you can use it as volunteering is one of the components to completing it
and a recommendation, an EPQ isnt really required by Oxbridge from what i understand but since you seem quite driven an EPQ would be a nice project to have and eventhough it wont lower the entry grade its a nice thing to write about, and might lower the endtry grade to your other 4 choices