If he was/were rich, he would have gone to college.
I don't see a problem with this sentence. It is not essential here to use the past perfect with "rich".
The use of the modal preterite "was" or the irrealis "were" imply that he wasn't rich then, nor is he now.
Like billj, I don't have a problem with the sentence. I'd say it's a normal mixed conditional.
The implication is that "he" isn't rich at the time of speaking.
I don’t see how it says anything about whether he was rich then.
If you want clear answers to your question in #1, you must specify the context.
Are you speaking about the past or present (If he was rich)?
Or are you speaking about the present If he were rich)?
In neither case are we told anything about whether he was or still is rich.
For me that's a clear yes to both assumptions!If he was/were rich, he would have gone to college.
As this seems to be Counterfactual, this implies that he was not rich at the time in the Past, so he didn't go to college.
What I want to know is, whether this implies that he is still not rich now, because "if he was/were rich" is used.
For me that's a clear yes to both assumptions!
In the absence of any context, in this sentence you're implying that being rich is a requirement for going to college.
It's semantic logic that dictates that he wasn't rich when he had to make the choice in the past.
If it's known that he is really rich right now, your sentence wouldn't make sense. In this case you'd normally say:
If he had (already) been rich back then, he would have gone to college.
Often we think of whether or not a person is rich as something fixed. It can be very difficult to escape from the situation you were born into, and in times past it was sometimes regarded as the natural order of things ("God made them high or lowly" as the hymn used to say). "If he were/was rich" need not refer specifically to the present, but could refer to all time; he wasn't born rich, he doesn't come from a rich family, he is not rich now and has no expectation of ever becoming rich in the future.
Because "If he were/was rich" refers to his never being rich, it can have an effect in the past, which is why the mixed 2/3 conditional is fine:
If he were/was rich, he would have gone to college.
However, a speaker who does not want to suggest that a person is rich or poor for life would avoid this timeless use of being rich or poor, and would refer to the person's being rich or poor at the time in question. Here it is in the past, so they would use the past perfect in a type 3 conditional:
If he had been rich, he would have gone to college.
A type 3 conditional says nothing about the present (perhaps he is rich now; perhaps he is not).