In my mind, the light is at the top of the list for importance. Then the tent and the fans based on the neighbors! But, all of the elements, nutes, EC/pH meter etc., are important, but the light for me is a central price of equipment that is worthy of research.
Also, the space you have is important to to consider. For example, I have loads of basement space which is great between April and October. The rest of the time it needs heated for the plants to thrive. I didn't know that until after I bought my first tent and the growth came a lot slower in the basement over the winter.
Now I want a bigger single tent for the basement year around. So, I am only heating and filtering one space/environment.
Also I can grow 5 plants legally. So, I am moving towards a perpetual grow and towards autos, as they are not photoperiods; so, I can have the light timers set the same for all the plants at all stages of growth.
So it has been a learning curve, for sure. And, I am buying more equipment as my grow skills build and plant numbers rise.
My advice would be to research lights and look for the package with the light you want. For example a 3x3 grow space can be covered for the veg with a 100 watt input (see
HLG 100, 3000k), but that led--assuming it is square--will only cover a 2x2 flower canopy. You will have to step up to a 200-250 watt input--assuming it is a new/effecient board to cover a 3x3 blooming canopy.
There are a ton of lights out there: I have
HLG 100,
Mars Hydro 2000 and
California Light Works SE 250 and I am happy with all three. They have great ratings, two are US made/assembled. And, all three have around a 10,000 hour life.
Sorry! Rambled a bit there!?
Tell us more about your current grow and future goals and I am sure you will get more advice from grower's, here.
(Also, I am not sponsored by anyone. So, I am sure there are other great lights out there, too.)