You might get a bunch of varying answers if others answer, people can be all over the place, but here is mine.
White is synonymous with European to me. If you are of European descent you are white, that simple. Of course you may then ask me that zinger, "Well how much percentage of the person must be European" as many do. One way to go is the Nuremberg Laws, although there are a good many Europeans that have very little to no non-white blood in them, and asking for only pure blooded Europeans with something like less than 5-10% non-White descent wouldn't be insane to ask. Europeans weren't admixed with blacks and other non-whites to hell and back in the past, purity in this sense isn't some far-fetched idea, it is how things were.
Within Europe there are a bunch of different groups of Europeans (Germans, Slavs, Mediterranean, etc.) and then groups within those groups, but personally I don't have any animosity toward any European. Though of course there are those that think of Slavs as lesser, and for some reason some even think Mediterraneans as lesser, but those ideas only divide the European peoples which is a bad thing.
If you want the truth for the absolute end goal of what I would want, it would be that the world only contained Europeans. There will always be separation by race, it must be removed if we are to look to our future. A lot of people may not agree with that, they just want people to stick to their own nations more so. I think that for example Africans are lesser and don't deserve the massive natural riches of Africa that Europeans could put to much greater uses. This of course would require a very great deal of violence, so there isn't any realistic way to do this cleanly. The cleanest way would be an Ethnic Bioweapon, which is in the realm of possibility, you'd just need people to actually want to create such a thing without raising suspicion and getting attacked by everyone.
The obvious composition of a white nation would be whites-only, European nations weren't full of blacks and arabs in the past. An all-white nation isn't some wild fantasy, it is how it was in the past. The best and most appealing way to achieve this is to just deport them, by force if necessary. But there are obvious harsher options if necessary.
There wouldn't be any contact with non-whites, there wouldn't be a need.
The difference in IQ between races isn't something to ascribe to, it is fact like evolution itself, generally I think of ascribing as implying there are alternatives. But I also agree that with IQ while mostly based in nature, the nurture aspect does have an effect. In Asian countries they have cultural differences that help encourage their intellect combined with their different schooling systems. The difference between Asian and European IQ is not that drastic either way, especially compared to the difference between European and African IQ. Another way to look at it is look at the achievements of Europeans and Asians then look to Africans and others. It would become painfully obvious once you see the differences.
With the mentally ill, I see them as tragic creatures, hopefully we will get to a point where mental defects and such can be weeded out genetically using technology so none have to suffer with mental deficiencies. My issue with the mentally retarded today is that quite a few are barely sentient, they could never live a regular life, and will always be reliant on their guardians which is a sad thing. "Retard blood" and "non-white blood" is an odd comparison, in a way there isn't much of a difference between a retarded white and a non-white. How are any of the absolute millions of Africans that are all borderline retarded or worse, any different than a white that was unfortunately born that way. In this case the Africans are normally this way genetically, and the retarded White is an unfortunate defect in the greater whole.
I'm unsure what else you might want to know, this is what I could rattle off real quick for you just of my personal opinions. I'm not 100% on everything here, but it's the best I could provide off the bat.