I'm trialling the French now on VH/VH. Having only used the English previously, I must say that the French are a much greater challenge to play as.

The key to surviving as France is focus. If you can get just one of Spain, Milan, or HRE as allies, and keep them allied by maintaining a decent border presence while also keeping relations above 'reasonable', then it's feasible to focus on whoever is your principal enemy. I find this is usually the HRE.

I also keep a diplomat near rome to make sure I can bribe the papacy whenever my ongoing fight for Charlemagne's empire starts looking a bit aggressive. So far, that works quite well.