If you're gonna use hops, might as well use Tor IMHO. I don't see the point otherwise since Mullvad is running the servers. Seems like an increase in latency for not much benefit.

As for locations to stay away from, no idea. Rule of thumb is latency shoooould be better if the location is as close as possible. So for me that's Hong Kong or Singapore. But the Great Firewall of China fukcs things up so that my latency is generally trash. I actually route my home through Switzerland.