May I ask whether the more third-party plug-ins, will reduce the FPS, thx
Some will, some won’t. It depends what they are.
In general though, the more you run with MSFS, the lower the FPS will usually get.
Some plugins will have little effect, but some a lot more. You can usually have a good guess though based on what the plugins are actually doing.
Generally yes the more you add they’ll nibble away at FPS all depends what it is some hardly make any difference some can take a big chunk.
So how do I know those plugins will lower the FPS
Because I’ll usually check the FPS before and after 
It’s not an issue if you have FPS to spare though a lot are worth loosing a few over but they don’t all have a noticeable affect some are really light on the system.