What is the most important component to consider while building a new system?

i would add further that i disagree with folks who say it is the source... that’s silly because it is all important, it is after all a signal CHAIN

what must be primarily considered is which component has the most impact on the actual sound being produced in the room, and that is always the speaker -- the physical transducer that actually translates the electrical signal back into something we actually hear

speakers, even very good ones, have the widest range of sonic differences (or some would say, the greatest variability of amplitude and nature of distortion from an idealized musical signal being sent to them)... and the speakers’ dispersion pattern interacts intimately with the room they live in and the listening position - so this is by far the greatest variable - by far

not that the source isn’t important... it is absolutely important... but you put up 5 $5000 sources versus 5 $5000 speakers in a given room, the speakers will provide the greatest differences in what the setup will actually sound like

There is no question that speakers are central to the SQ.
However, the source can make or break a system. I once heard a million dollar system with a very digital edgy sounding CD player and I wanted to run out of the room screaming!
When I got my long searched for Woodsong Garrard 301, I wound up upgrading every part of my system. Only now do I have a destination rig. And the greatest and most significant upgrades were to my front end-TT, arm, cartridge and preamp with phono stage.
Garbage in, garbage out! Great “food”, great “meal”!

Another way of view: The order of cost for each component from most expensive to least expensive.
1. Speaker
2. Amp (power + pre)
3. Source (turntable/CD player)
4. Cables
That is how I spent for my components. 

Dollar amount can be a way to prioritize but I think that is a kind of different question than what is being discussed.  I certainly believe it is the speakers that is super important and how they perform in the room they are used in.