brdy

This kit from ThermalTake looks like it might work. It's a bit pricy, but it looks to be very good quality. 

So far as I know, AMD has not released an official statement on when Am4 will come to an end. The concrete information we have is through 2020, as announced back in 2018
 
This is what makes the upgrade path part speculative. It's entirely possible for the 5000 series (if they continue with their naming scheme) to be on whatever will succeed AM4

Depends on the games you will be playing and the settings. With your gpu reaching 144fps on most new games would be difficult even at lower graphic setting. So i advised you upgrade the gpu if you want to fully utilised the monitor.

If I was in your shoes id get a whole new rig im not sure how good that GPU is maybe someone else can say that
I think it would bet better to get on the current gen systems. especially for 144hz

i play Call of duty, GTA V and other like that. I play with the setting on medium at the moment and currently getting 60fps 

If you play newer games, no.
You would probably want to go up to at least a 2060

use this awesome liquid that is available nearly anywhere and you probably have it in your home, its water!!

There are no pearlescent fluids that are anywhere close to worth recommending at the moment. They will all cause a larger headache than anything pastels can provide even on a good day. If you want a visualization of flow, a flow meter is the best you can get without very high risks of precipitation and clogging.