Actually, now that I think about it, Senko going after the Power of the White Snake first might make more sense than anything else, especially since it is a passive power that wouldn't be affected by her unbalanced chakra... And the healing factor might help her survive the grafting process.
And she's primarily a hand to hand melee fighter, so it does kind of make sense if her initial "enhancement" are things that make her more "tanky."
So once Men-Ko is introduced, when Senko isn't collecting samples or doing research... Or on missions, she'd be training in strengthening her will and resisting Genjutsu so that she can eventually go to the cave, pass the tests, and get the White Snake Power.
Then grafting.
Then learning her own Sage Mode.
Then, when she has time, going back to the Cave to finish her training and get Snake Style Sage M.
I'm also starting to think that, while she'll be collecting DNA samples all along, her initial grafts will be things that improve her role as a melee fighter via either more melee options, better tanking, or things that provide support(Increased mobility and the like.) Elemental releases will, when possible, come after Sage Mode unless I can justify it ending into melee.
I'm still leaning towards White Snake Power not counting as a mod for the sake of balancing her chakra.