I don't think that I need to have unjustified belief in any of those things. My belief that there is an outside world is an irresistible intuition, but I am justified in believing that it is there, or that assuming that it does is a good plan. It's based on the evidence that making that assumption has been profitable. What more do I need to support that belief and call it justified. Assuming that others are conscious and have experiences is also a justified belief, as is using formal systems to my advantage.
It's all about what works. If an idea works - if it explains a portion of reality and helps me anticipate.some aspect of it, the idea is a keeper, meaning justified. I like this anonymous Internet persona's take on the matter:
"All we need to know is that we have desires and preferences, we make decisions, and we experience sensory perceptions of outcomes. If a man has belief B that some action A will produce desired result D, if B is true, then doing A will achieve D. If A fails to achieve D, then B is false. Either you agree that truth should be measured by its capacity to inform decisions and produce results or you don't. If you agree, then we can have a conversation. And if we disagree about some belief, we have a means to decide the issue."
Notice that even if we knew that the outer world was an illusion - some sort of matrix or vat-in-a-brain scenario - nothing would change. We would expect to be subjected to all of the same rules that existed before we knew that. What should you and I be doing differently if we knew that there was no external reality, or that the one we think is there is not? Nothing that I can tell.
So what faith do we need that it is there? Why would we care either way? Sure, we'd be shocked, but then what? It would be life as usual as the guy above describes it. Pouring a glass of water and drinking it would presumably still relive thirst even we knew that there was really no water out there, or that we didn't really have a physical body.
My beliefs are all justified by prior experience as far as I know. I have no use for unjustified beliefs.