I think it’s great that you are asking for advice from the community on building a computer system for the sim. Perhaps you are starting from scratch, moving from Xbox to PC. Or maybe you want to upgrade an existing PC.
I enjoy jumping in and offering my advice (for what it’s worth.) 
I would ask you to provide some information that can help make the process easier.
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What is your budget? Do you have any ‘wiggle room?’ It’s very hard to spec a computer without that info.
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What PC hardware/software, including your network/internet components ( if any) do you already have? Are you planning to migrate that hardware/software, or simply start over?
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What components are you focusing on now? Do you have a CPU and/or GPU in mind? It’s much easier to advise someone when certain baselines are known.
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What kinds of aircraft do you enjoy flying? Do you plan to add a lot of 3rd party content? Computer horsepower requirements can change dramatically depending on whether you are content flying mostly GA, or want to get into more complex and performance challenging aircraft like Fenix airliners.
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Do you intend to use VR? If not, what about the size and complexity of your intended 2D cockpit? Three 4K monitors plus several smaller monitors for panel popouts stresses a system far more than a single 2K monitor, and knowing your goal in this regard is crucial to system design.
Bottom line, the more info we have, the more we can help you make good choices. I say we, because there are many here with as much or more experience than I have who are willing to help.