how to manage DB connections

Hi If so how do  Team,
In my CI3 app I never worried about this because we autoloaded 'database' lib.
In CI4 it seems I now have to connect in my code - I have chosen the constructor of any Controller or Model where ever I need to access the database.
I am now aware that I could hit connection limits (currently 151 by default for mysql db)
A few (perhaps) obvious questions:
1) If I make a connection in a controller and the user session redirects to another controller will the $db persist for the session or do I open a second etc connection?
2) Should I check for an existing connection in each constructor and either proceed or open a new connection as appropriate? If so how please?
3) Another potential strategy would be to force a disconnect on completion of my db interation. If so how please?
4) I quite like the freeQuery() call. Is this recommended to optimise memory as lng as you don't need the cached result?
I have read the upgrade notes carefully but haven't found those nuggets yet.
Appreciate any thoughts and guidance.
TIA, Paul

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Sorry typo in first line ...groan