Plantinga is absolutely wonderful as a person, as a Christian and as a philosopher. He is a model for other Christians in the field. The paper on omniscience to which you refer is, as I recall, good. My only memory of it is that he argues that even if we can give no account of how it is that God could know the future this is not a problem because (a) we know that God, being omniscient, does know the future (because an omniscient being would know of any proposition whether it was true or false and there are such things as propositions about the future), and (b) we cannot give an account of how God knows the past or the present and nobody thinks that this is a problem. I may be completely misremembering the article as it was about 10 years back I read it.
The idea of basic beliefs is not daft - it simply refers to beliefs that we hold that we do not hold on the basis of other beliefs or on the basis of reasons. For example, I may believe that there is a keyboard in front of me now. I do not believe that on the basis of an argument - I simply find myself believing it in certain situations (i.e., when I am appeared to in a key-board kind of way). Such beliefs are basic and, if it is not irrational to hold such beliefs then they are properly basic. What is controversial about Plantinga is his longstanding defence of the claim that for some people belief in God can be properly basic (i.e., rational to hold in the absence of any arguments or evidence).
I did once ask him what he thought about universalism and he avoided the Q. Tom Talbott tells me that Plantinga has some sympathy with the idea of universalism but I don’t know how much.
I don’t agree with him on everything but he is stunning!