I agree that speakers should come first and it is essential that you get them properly placed, hopefully in a properly treated room. I would then consider a preamp or if you’re inclined towards an integrated that would be next. I like separates, probably most people here do, but there are some advantages to integrated and I think just in the last few years, there are some really good ones that have come to market.
do your best to listen before you buy, and in your own room if that is possible which is not always the case. Folks will usually suggest what they have bought and that can be helpful, but this is incredibly subjective. A sound that pleases me, may not to be to your taste. It took me longer than it should have to learn that simple fact. I would be looking for equipment and people I respect would say oh that’s too bright or that is veiled and I would think that’s not at all how I hear it. There must be something that I’m missing. It turns out that we all just have different taste and you should trust your own ears. Some people like chocolate and some people like strawberry.
I’ve remade my system a couple of times over the last fee years and three changes made a really substantial difference: 1. A significant upgrade in speakers. 2. A significant upgrade in the preamplifier 3. Getting my room properly treated
Other upgrades have brought improvements, but far more subtle than these three. That’s been my experience, others may differ.
Good luck and keep us posted on what you do