Very much agree with your future-proofing idea. Experience has tought me that anything not on my hard-drive will eventually give me a headache.
For images the “Local images” plugin is great. It will fetch all images linked in your vault, stored elsewhere.
For text (for example articles I read), I keep a local text copy in Obsidian, but exempt them from Search and Graph view, setting under “Files & Links” > Excluded Files. I use Archive, old stuff I might need in the future, text files take no space for practical purposes, no reason not tho keep them forever. Old Images do take some space, but that one image I needed after a year outweighs the costs
I am testing to keep older static items in yearly folders, Obsidian doesn’t care where items are. I hate seeing folders, but moving things out of the way while still having access to them is great.