I’m not based in the US, so take my comments, as far as they refer to your son’s high school schedule for what they’re worth.
For Oxford, the three AP 5s in Calc BC, CS and physics are non negotiable. So his schedule in the year(s) he is taking them should reflect that.
I’d put the same emphasis on AP physics 3 and linear algebra, if he can take the AP exam for that - it appears it is offered at your high school, but not as an AP class? Oxford is fine with self study for an AP, in fact it reflects the qualities they are looking for quite well.
So in the years he is doing AP maths and physics and CS, I’d look carefully at whether taking another two classes at community college in those subjects will inspire and energise him, or rather exhaust and burn him. Yes, we’ve talked about how much maths his competitors in the UK are doing and how he can emulate that, but he’s still got reqs they just don’t have. (Some kids feel absolutely exhausted by the social sciences, so there’s that…)
You said you want him to keep his US options open, UIUC and others, so in your case I’d make sure to identify those now and, before dropping foreign languages and the social sciences (isn’t it three years of FL at high school rather than level three which is required by most colleges?) make sure he’s not losing opportunities he might regret.
Hard to prepare for both, I know.