I haven't thought much about the first question, but to answer the second, I've already transcribed all the Chants from the Solesmes Graduale Romanum 1961 (which I think are almost identical to those in the Liber), and I'm now transcribing all the Antiphons from the Liber Usualis.
So 'we' almost have a Liber! and 'we' have a Graduale. Note the texts needed can be found here, http://www.clerus.org/bibliaclerusonline/en/index.htm The side bar has a section on Missals and you will want the 1957 version, the text is easier to use than the 1962 version. Note there are a very small number of typos!
For the Graduale, yes, I have most of the Propers ready to assemble for the Solesmes 1961 edition, and I've converted the GABCs for the 1908 Vatican Edition (though they still need proofing). There's just a few Masses, eg. Easter which are a bit complicated and very involved. For the Liber, not yet, I'm maybe half way there, I don't have the Antiphons ready yet, though most of the work on the Liber will be adapted from my work on the Graduale. The plain Texts (Collects, Secrets, etc) i.e. those not set to music can be found in a few places on the Internet.
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