Fat over lean in extended painting sessions

I'm working on a new painting, which I quickly discovered is way beyond my abilities. Long story short, I think I'll need to go at this in several sessions. It's full length, so I expect to be doing a hand here, a foot there, with tweaks in the coloration, halftones, etc.

So, I'm concerned that I'll be working in enough sessions that the fat over lean rule is going to be a problem. How do you control the fatness of paint in later situations, if you don't really know how many layers you're going to need?

Here's what I want to do, is this going to be a problem?[list=1][*]Thin underpainting in one session based on color studies, using paint + 50% Turpenoid and linseed oil mixture. The ground is a non-toned titanium acrylic gesso on panel, with a graphite drawing.[*]Second semi-finished layer using paint w/no additives[*]Third touch-up layer using paint + several drops of linseed oil, premixed on palette[*]Fourth and so on using more linseed oil until I finally give up and start over[/list=1] All of the paintings I've done so far have been in 1 or 2 sessions, so I don't usually worry about this. I did look for this question in the archives (searched "fat over lean") and didn't find it. I'm actually embarrased to ask, since it seems I should already know.