What should I do as a rising junior? (For summer + junior year)

So far I have an unweighted 3.94 GPA, attend a cyber charter school, and I'm a dedicated painter (did around 24 paintings) and have done research (basically on issues with organoids, molecular pathways, etc). As for coursework, I have 2 APs (AP US History and AP Human Geography) and 5 Honors classes (Honors English 9, Honors Algebra II, Honors Biology, Honors Chemistry, Honors English 10) down because I decided not to take the AP grind since I focused on research and painting.

Some schools I want to go to are JHU (Johns Hopkins), Princeton, Brown, and Cornell.

I thought of this:

1. Start a research project on Polygence

2. Do some SAT prep

3. Do some ACT prep

I'm considering on taking both the SAT and the ACT. But at the same time, I was loosely thinking of Polygence. I want to avoid burning out from the sheer weight of these. Should I focus more on the SAT/ACT prep or should I start on Polygence?

Also, what are some test strategies I can use to get an ideal score for universities like those?