Advice for wash and care with little effort

I don't know if you need to worry about corrosive road treatments there. In some parts of the USA the roadways are treated with mineral salts to artificially depress the freeze point of the surface. That's the biggest reason we also have demand for anti-rust treatment.

Toyota's materials selection and anti-corrosion finishes are quite good overall. Don't sweat the anti-rust unless you are storing the car in a humid coastal/beach environment and/or know that your roads are being salted.

Beyond that, find a good local car wash and buy a subscription to save a bit. Your general idea and schedule should work fine to protect the car.

 

I think your plan makes perfect sense.
Monthly car wash and semi-annual polish.
Actually once a year would probably be enough.
Gauge by eye.

Forget rust proofing and undercoating. It is mostly a scam.
Sometimes it causes more harm than good.

 

I went looking for things to spray with Fluid Film (rust inhibiting spray), but I didn't see much. Maybe some suspension parts. Everything else under the car is covered in plastic panels. I don't think you need to worry about it.

 

That's more than what I do on most of my car. I have read here that automatic car wash during winter may not help much for getting rid of salt for those waters are filtered and reused, thus contain dissolved salt. I stopped washing my car at automatic car wash because of that. But it is impossible to wash car by hand on the drive way during winter. So, my car care entails several hand wash only during warmer month of year between May to Oct. I have never waxed my car other than the spray wax applied at automatic car wash. I did buy a bottle of spray wax recently for my new 2020 Prius Prime, but have not used it yet.

As for the under body rust proofing, as @m8547 said, there aren't much areas that you can treat, unless you spends a lot of money to remove all the under body covers.

Yap, for my 2017 PRIME, I took it to a FluidFilm applicator shop and they told me they basically told me I don't need it and they can't do it with all the covers. I did apply FluidFilm can spray around suspension after two winter, but I sold the car not too long after that. I plan to apply FluidFilm (or equivalent) on the suspension and few other exposed area under the body of my 2020 PRIME before the first winter.