Maybe we do it the other way round:
you tell us what you want to do as DIY or backyard hack mechanic and what you have available in space or something else for the repair. For example a roomy garage, a carlift, jacks, or other items.
To what expends do you want to repair. Just simple things like replacement of the usual wear parts like air filter, oil filter, spark plugs.
Or are the the one who disassembles half an engine?
Any knowledge about car electrics / electronics?

Do you have repair book/manuals?
I would start with buying for example a Bentley repair Manual, read it carefully and then decide what you think you can DIY or not.

There can be an endless number of tools one can buy, but it all depends what skills and what other surroundings for repairs are available.
My wife always says to me, we already have 2 or 3 of the wrenches. And my reply is always, yes but I need one with a little shorter handle , this or that.
You can spend a furtune on tools, which you might only use once in your life.