Single instance of reusable HttpClient
You don't need multiple instances. In fact, HttpClient is designed specifically to persist and be used for multiple requests (see: HttpClient.DefaultRequestHeaders).

There's already a lot written about this so I'll redirect you to those resources:


Do HttpClient and HttpClientHandler have to be disposed?
Is HttpClient safe to use concurrently? 
What is the overhead of creating a new HttpClient per call in a WebAPI client?