Cleaning and re-installing a crank As a result of needing to replace a chainring ( Worn out chainring or missing tension ), I'm about to reinstall a crank, and would like to clean it before doing so.
Regarding the next picture, can I:

clean outer (1) with soap for dishes (rinse), and before installing it, apply a very fine layer of all-purpose grease (conforms DIN 51802,  DIN 51825 part 2 and NLGI-class 2, made for long term greasing of motor and machine parts, specially for fast moving bearings)

clean inner (2) with rinse and scrub it with a plastic brush designed to clean drinking glasses, then apply very little grease to the thread

remove (3) the sealing ring, scrub the black, flat surface (update: I thougt this black surface was grease mixed with dirt, but no, it is clean black-painted metal) with rinse until it shines, then apply grease to it and put the seal ring on again.

apply (4) Loctite 243 to the screws of the smallest ring, since it originally was super hard to open and had this green stuff in it? Loctite 243 is red, apparently it can be used everywhere on the bike (I've never used it in my life and have a new one unopened). The outer and middle ring had no green stuff applied and were not hard to open.


Specially (3) is what worries me a bit, maybe it is better to leave it as-is


Next two pictures, what and how should I clean and grease something there? I've labeled parts for you to make easier references in the answer. The bike has a SM-BB52 bottom bracket.
Right:

Left:

I'm a bit embarrassed about the dirty frame.
What are things I absolutely should avoid doing?
I do have &quot;chain cleaner spray&quot;, &quot;break and parts cleaner spray&quot; as well as isopropanol 99.9% at hand.
I think you may be over thinking this a little.
Firstly if you're going to take off the crank for cleaning you should probably remove the BB as well.
The Shimano manual covers what to grease and what not
https://si.shimano.com/api/publish/storage/pdf/en/dm/FC0002/DM-FC0002-13-ENG.pdf
Basically remove the BB, clean inside the shell with a paint brush. The BB isn't maintainable so you just wipe it off, and if there's play you throw it away and replace it with a new one.
Removing the BB and greasing the threads will help prevent water ingress, and you want to remove the BB about annually to stop things seizing up.
Generally I soak metal things (chainrings etc.) in petrol and it gets them clean. If you are eco-friendly you can probably find a greener less explosive degreaser. Anywhere you have rubber seals then petrol is likely to kill it, so avoid. Plus anything you can't re-grease you shouldn't degrease. So the bearings inside the BB are something you want to avoid getting any kind of cleaning agent into, so don't soak your BB in water or whatever, because that's only a good idea if the BB is user-serviceable which it is not (if it was user-serviceable you could fully degrease and then re-lube, but that's not the case). After cleaning metal parts in degreaser, rinse in water. No soap. Grease on parts that move or get tightened.
The chainring bolt torque is in the manual, 12-14Nm for the big/middle ring, 16-17Nm for the small one. The loctite will reflect that extra torque. Green loctite is the weaker one.
If you relate the 5mm bolts to the required torque, the function of the Loctite should be obvious

because 5mm bolts aren't typically good for more than about 12 Nm. Green loctite is wicking and it has a relatively low torque to break away (10 Nm), which is why it's not too hard to loosen, but has a higher prevail torque, which is the torque required to rotate it 180 degrees. Red loctite is much harder to break.