New 04 civic lx owner, michigan

[doless]

Hey there, 22 year old michigan native here!

Well i've been looking to buy a more frugal car for a while (my wrx gets mid 20s on 93oct if i drive it like a grandmother, and that defeats the purpose of a wrx.)

So just last week on a street by my apartment i say a civic, has some scuffs here and there but no rot/rust underneath/on the quarter panels, just one hole in the bottom of the hood.

Contacted the seller, came to find out his daughter was the only owner and he was selling it to buy her a mini (she just finished grad school)

He is also a garage mechanic (full time bodywork guy) but has an awesome garage with a few porsche 944/old mercedes and a sweet lift in it, so i stopped by to check it out.

Oil done synthetic every time, air filter is new, newer battery. No leaks or such anywhere in the engine bay.

He told me the front end was making a noise when he got it back from his daughter at 70k miles (she hadn't driven it due to not working a job and living on campus for over a year) so he had sat out there, drank beer, and replaced the timing belt/water pump, new front links, and clutch at 70k. Also has new tires and brakes on it. The noise didn't go away and he tracked it to a bad input shaft bearing and went and bought a used 35k miles trans and put it in.

Car drives perfectly, no noises, super smooth clutch/trans, brakes are great, tire's have at least 50k miles left (60k mile tires) no rattles or anything (typical honda stuff), the only thing i notice is over bumps a little chink from the front right. Suspecting a loose end link or possibly a strut, i'll get it taken care of before winter.

I paid $5200 for it, had 81k miles (just turned 82k).

I'm not exactly new to hypermiling, when leasing my scion frs i constantly coasted and such to get over 34mpg on my daily city-ish commute, but i'm always ready to learn more and such.

The biggest question i have is at what rpms does my car use fuel/not use fuel when downshifting to break? I've been doing it more and more recently, i used to just coast out of gear and use the brakes, but saving break pads/gas seems more tempting.

Also any tips on rustproofing the undercarriage/wheel wells? Our michigan winter/salt roads are absolutely brutal on cars.

thanks!