I posted above before I'd read this -- I'd really stress again that, at least in the humanities, writing is the difference between mere 'accumulation of knowledge', which we all know will eventually be forgotten, and understanding. I would actually recommend Umberto Eco's book How to Write a Thesis as a great foundation for how to structure your cross-disciplinary studies and synthesize, again even if just for yourself. If you do start a blog, however 'cliched', you can also start to seek validation (or, even better, critical commentary!) from individuals in your fields of interest.

It feels very 'old internet' and his particular objects of study may not be of interest to you, but http://www.autodidactproject.org/ is the very interesting record of one man's lifelong studies outside the academy, as well as reflection on that process.

Best of luck! Certainly ignore those who say this is no different than watching TV if you feel a genuine 'conatus', i.e. striving and desire, for these pursuits.