I think Kosher Jesus is a candid account of the true life of a Jewish man told unabashedly drawing historical evidence of the Jewishness of ריבי יהושע from the very Christian writings which have been used to refute his devotion to תורה for hundreds of years. What I enjoyed most about R. Boteach's work was his ability to discredit Paul the Apostle with fair and concise criticism giving him an honest judgement as a charismatic eloquent orator but also as one who was not as well educated in תורה as he professed to be.

As a side note, I was taken aback by his adamant statement that the Jews can never accept even this historical figure as the משיח based on certain criteria not being met. Does this mean we cannot truthfully call ריבי יהושע the משיח בן-דוד until he indeed fulfills all the criteria?

I haven't read this book so I can't comment on the historical (in)accuracy; indeed, nor even on the validity of the approach employed by Rav Bo•teiꞋ akh. "De-Hellenizing" the Διαθηκη Καινη (NT) is fraught with problems. Certainly, discrediting Paul concurs with Eusebius' record that the N^әtzâr•imꞋ  considered him an apostate and my research finding that he was excised from the N^әtzâr•imꞋ .

What you wrote implies that both Rav Bo•teiꞋ akh and you employ ambiguous or conflicting terms describing the issues surrounding the משיח. If Rav Bo•teiꞋ akh argued that ריבי יהושע cannot be "the משיח" then he has erred. To further confuse the issue, your question about the משיח בן-דוד is an entirely different issue! Rav Bo•teiꞋ akh has a valid argument for not (yet) accepting ריבי יהושע as the משיח בן-דוד. There is an enormous difference, at the very least timewise, between the משיח בן-דוד and the משיח בן-יוסף.

It is our contention that ריבי יהושע has satisfied, and is the only possible candidate who could ever satisfy, the specifications for the משיח בן-יוסף. We expect that the one and same person will also be the משיח בן-דוד, but that remains for time and events to demonstrate. Certainly, no other candidate can ever meet the Biblical qualifications. It will be ריבי יהושע or no משיח בן-דוד – ever! We think the a priori of that statement of fact makes a compelling argument. But Rav Bo•teiꞋ akh is technically correct that the latter hasn't been demonstrated yet.

This is covered rather exhaustively in our Khav•rutꞋ â – and it's again in the notes of The Netzarim Reconstruction of Hebrew Matityahu (NHM).