If you are getting good results with the alkaline bath you are good to go, you dont even need to "neutralize" the print afterwards. Just wash it and leave it as is.

pt/pd printing benefits from an acid media, this is why the oxalic acid bath trick is so useful. GIven that you are usign fixed out paper, I do not know if this applies or that if you would benefit from giving the paper an oxalic bath. If you are getting good results with now, dont mess with something that is working.

Certainly the paper will have the same archival properties that a regular silver print has. So dont worry about this issue, just do your 3 clearing baths and you should be ok.