He should definitely do a 4th year of science and if he is not interested in doing more than the minimum for graduation that might indicate that engineering is not something he should pursue as there will be a LOT of science for pretty much any engineering degree. He should also plan on that 3rd year of Spanish - some will overlook not having a 4th, but most do want to see 3. I think most will count econ as social sciences.
We had a slightly different take on early list building. It was honestly way more about narrowing down things they liked and didn’t like in a school and opening their eyes to there being more schools than the 10 they know now (which will inevitably the flagship and all the reaches). While it’s true the change a lot in these years, starting for getting a feel for what they like we found to be helpful at this age.
Best of luck to you!