What to do for 8 months before Starting Strength? P90X?

Having read this subreddit and its FAQ, I would like to begin the Starting Strength programme. However, for reasons I shan't get into, I can't join a gym until September 2012. Until then, I will only have access to dumbbells, a pull-up bar and my humble bedroom floor.

I am doing what I can to 'get fit', and am currently following the Couch to 5K programme. I have also embarked on a healthy diet, having completed a few months of keto. However, I would also like to work on increasing strength/muscle-size, and am eager for these 8 months not to be wasted.

I also like the idea of a regimented plan (as with C25K), and thus all things considered, P90X seemed like a good fit. However, I'm concerned by how the exercises/'science' behind P90X seem at times questionable.

My question: Is a 90 day round of P90X a good way to prepare for Starting Strength, improve fitness and build (some) muscle; or, would a focus on barbell routines and/or Convict Conditioning style exercises be a better use of my time?

I appreciate that one programme cannot tick every box, but if any of you would care to comment/advise on P90X or other programmes that fit the bill, I would be much obliged.