1 - Let it cool down first. If the fans aren't blowing while it cools down, the heat can creep up into the heat break, causing clogs. Cheap to fix, but a pain in the butt and really, unless you're sitting watching your prints, you likely wouldn't notice 5 or 10 minutes to cool down.

2 - This comes down to personal taste and if you have any issues to solve with adhesion. I don't have any adhesion issues, correctly leveled, and do not use any adhesion helpers like glue stick. I clean my bed with IPA about every 5 - 10 prints, but don't bother every time. If I see any adhesion issues, I try cleaning first with IPA, if that doesn't work, soap and water then IPA.

3 - Depends on how much humidity in your area, and what kind of filament. I'm on the prairies and just leave it on, even if it takes me a month or 2 to finish a roll. I've done this with PLA and PETG without experiencing any issues, though I've read that certain filaments are more hydroscopic.

4 - Spares to have on hand would be heater cartridge, thermistor, nozzles, maybe a spare hotend, and it wouldn't hurt to have a spare bowden tube (look up Capricorn Tubing for this). If you're looking for upgrades, look into the yellow bed springs, but other than that, learn the printer and see what issues you may want to solve before buying a bunch of upgrades you may not need. That being said, when you get tired of the noise and want to go more silent, do not get the Creality silent board, it is still an 8 bit board, instead look at the 32 bit BigTreeTech SKR Mini E3. There's a good chance that will be the first upgrade you will want besides the better springs and tubing.