Many types of filament go brittle with age and moisture. Leaving any sticking out of the top of the hot end is unwise. However, unless you are using something more exotic than PLA, you don't need to do more than eject the filament normally, as the remaining aged PLA will be purged when you recommission the printer.
Oil and grease attracts dust. I'd clean as much as possible off exposed surfaces before storing it, with the expectation it will need a thorough clean & lube on recommissioning it. Shrink wrapping or bagging in plastic to exclude dust is advisable. If there is any risk of condensing humidity or sub-zero temperatures I'd use a light wax anti-corrosion spray, but check the spray's technical data for plastics compatibility and removal instructions.
It certainly wont hurt to slack off the various belts' tension till they are quite loose to reduce the risk of the belts taking a permanent set round the pulleys, or the tension cracking any plastic frame or tensioner parts.
The one big thing you've missed, that may be applicable to some types of printer is:
Remove any wheels in the mechanism with rubber or other elastomer tyres so they don't develop flats, and store them wrapped in acid free tissue paper in a sealed plastic bag. If there were traces of oil or grease on the tyre, there's a risk it will degrade in storage and need replacement.
Remove or de-tension springs in extruders with plastic structural parts. I wouldn't bother if its got a metal lever arm and body.
Write a checklist of what needs doing to recommission it as you decommission it. Save software and settings to a thumb drive. Store both with the printer. Also, it wouldn't hurt to do a test print before decommissioning and bag and store that with the printer so you've got something to compare with if you have quality issues on recommissioning.