My impression is that the Go team had two targets, both based on languages in common use at Google: C++ programmers, and programmers using languages like Python who wanted more type safety but didn't want to use a language with a massive ecosystem.

I might have misunderstood the last part. Why would anyone not want a massive ecosystem with their language? You can always ignore the ecosystem while retaining the option to change your mind later.

Not much actually, the developers of Go mainly wanted shorter compile times than C++ offered.

Pretty sure different people wanted different things. Some people certainly wanted better concurrency.

Sure, that too. Both of which however had little to do with Java.

There is nothing on GUI side in Go and it does not seem to be priority of core team.