That housing crack is a challenge I would consider accepting. Can you fashion a metal strap to fit on the backside to bear on the plastic and keep it from flexing? I Googled "gluing chainsaw plastic" ... If the backside of the housing has webbing that will not allow a strap to be fitted, then...
A lot of us on a popular 5th gen 4Runner forum have removed the bypass spring and standpipe from the OEM plastic housing and installed it into a genuine Toyota metal housing PN 15620-31060 to make it the correct height. The standpipe tabs have to be bent to changeover to the metal housing even...
I would buy OEM. Powergrip clamps have to be replaced when removed. Will you ever need to replace the radiator? OEM clamps are reusable. If you ever need to remove a radiator hose, you'll have to buy a Gates hose clamp removal tool to remove the clamp without damaging the hose. The tool costs...
I live in Phoenix, AZ, which is well known for high summer temps. I use 5W-30 all year in a 2011 Toyota 4Runner even though 0W-20 is recommended in the USA. The loss in mileage is less than 0.10 MPG. Toyota recommends thicker oils for this vehicle in foreign markets.
It's great to see your son's desire for multi-discipline studies. Encourage this. I pursued three degrees, mathematics, computer science and mechanical engineering, which altogether helped me to be a much better engineer (now retired).
Your son needs to be proficient in trigonometry before starting calculus. It may be useful to study pre-calculus to review the important concepts of algebra 2, trigonometry and geometry before starting calculus. You'll find more information in a Google search
I'm interested in the technology Toyota can develop in terms of hybrid reliability, vehicle safety and bring it to the consumer market with competitive cost of ownership.