Honestly, depending on the sim you choose, you're gonna probably gonna struggle to power five monitors on that budget. Graphic cards are ridiculously expensive at the moment, especially Nvidia. I'd personally wait and see what AMD come out with soon and what Nvidia has lined up to compete. Also, if you intend to play MSFS 2020, wait and see what the system specs are for it.
Hardware-wise it all depends on what type of plane and style of flying you like. I've realised there's no really no one-stop shop for all flight-sim hardware. Like on a site like simmarket.com you can purchase a Force Feedback Cessna Yoke for $1895 (and prices quickly escalate!), or you could 'make do' with a Thrustmaster T.16000M FCS Hotas for around $130 (I still need to add the throttle unit) and still have a blast.
It sounds like you have a hardware cockpit type environment in mind. That's way beyond my means, but then I was never a pilot and have nothing to compare my experience to. Any other questions, feel free to ask.