Should I use Unreal Engine 4 networking API or create my own external server or use open source solu

I am working on online multiplayer FPS on UE 4 with up to 16 players. I am now at the making architecture model, stage. I am doing research on possible server architecture model with respect for future scalability, bandwidth support etc. However I could not find any good information on how UE 4 networking work and what it’s architecture. In order to know whether it will suit my needs and whether I will be able to modify it

Is there an UE 4 network API so that I can connect my custom web server to it ? Does it help to solve common errors like Lag compensation, Fireproof player etc.?

UE 4 by itself is a client & server package already. No need for a custom server program.