I'm thinking of doing a playthrough with no missile/energy pickups, because I remember this game being really easy to beat on just one E-Tank. Of course this also means missing out on most of the OOB/rocket-jump time saves, but it's a catagory I feel confortable running. Would this fall under Any%?

Hello there, I'm probably the last remaining active speedrunner of this game so I can help you with your task if you are still interested. This would probably fall under what we consider low% because of how the game calculates %. It would be a tough task to go for the lowest % possible in game. Skipping every expansion is definitely possible because you can refill your UA on every boss that requires UA to be killed. Sadly there is no humanly possible method to skip weapons at this point in the game.

Here is a video with some skips that could still be used with limited missile ressources

Sorry for late answer.

Good luck