Do you belong more to souce first or to speakers first school of thought ?

Speakers first, always. Only you have your ears, specific musical preferences in what sounds good and the environment they will live in.
Go with the objective of buying something you can live with for decades, source equipment will always be swapped as improvements or budget improve.
Had my first pair for 30+ years and cycled through 4 systems and they just kept sounding better.
As for GIGO, you can't drive great sound thru bad speakers but the opposite holds true. Great speakers will always sound good and make the most of the source.
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Speakers first. Buy the best speaker you can afford to match the room. Buy source with the remaining budget.  This will give you the best sound from whatever your source may be.

Then go on to upgrade the source and other components to match the speakers. 

Once speakers and source matched upgrade the speakers and start again!

Wrong. Get the speakers you like most and put them in whatever room you've got. Next year you might move to a better place with better listening room and you wouldn't have to replace speakers.

I was just browsing through the amps and preamps forums, and came across this from @atmasphere 

If your preamp or source is lacking, it will not matter how good your amps and speakers are- they cannot make up for signal loss or coloration! The preamp has to be right!

from @atmasphere 

If your preamp or source is lacking, it will not matter how good your amps and speakers are- they cannot make up for signal loss or coloration! The preamp has to be right!

Very true! 😎

Mike