I don't precaot with oxalic when using Platine. I have found that Platine will make good single coat prints, but the paper really does look better when double coated.
However, doule coating has been difficult for me, as I have found that rod coating produces completely unacceptable tone 'grain' and I get a similar problem using Hake brushes. I even tried rod for the first coat, and Hake for the second.
That all changed when I started using the Richeson 9010. I'm now completely satisified with double coating for this paper, and also Cot320, which is very similar.
I did some tests pretreating with oxalic, and I didn't see an improvement in the paper with this step. In fact, due to the extra step swelling the paper fibers, I recall I was getting a slightly worse single coat after the oxalic acid pretreat.
Ultimately, you need to find your own method, because what may work for one, may not work for another due to environmental conditions or other differences. So you might want to try a few tests to see for yourself. Take a sheet and precoat half with oxalic, and then let it dry. Then coat as normally, and see what the differences are. They should be readily apparent in the print or test strips.
FWIW, there has been some speculation that in some cases, the oxalic isn't really the issue, it's the H2O that is being introduced. If the humidity is low in your workspace, precoating with distilled H2O is similar to creating a localized moist envoronment, which will definately affect the quality of the coat.