A Jewish army in the XI century establishes an empire that stretches from Afghanistan to the Mediterranean and includes the Holy Land?
I don't care how plausible that is, something about that gives me a tingly feeling....And I'm not even Jewish.
I'm not a specialist on the subject but, AFAIK, Judaism is, in general, not about the conversions: the Deity selected
specific tribe as his/her/its "chosen ones". In the case of the Khazar rulers it was possible to come with a genealogy (no matter how shaky) covering a reasonably limited number of the individuals but doing the same for a huge number of people would be much more difficult. In other words, I'm not sure if, even with all of them accepting Judaism, the term "Jewish" would be applicable (just a nitpicking).
There are a few questions though:
Would they establish Jerusalem as their capital and would they rebuild the Temple?
What would their relationship be like with the majority Muslim population in the territory they ruled?
They could have Jerusalem as a religious center but it IMO would be somewhat difficult to link this empire to the old Jewish state. OTOH, I may grossly underestimate the theological part of the issue. As for the relations with the Muslims, there was no UN and the endless human rights groups to complain to so the subdued population would have to behave, as it did under the pagan Mongols or Christian Russians.
Would they be more or less hostile toward the Byzantines than the Muslim Seljuks of OTL?
Constantinople was a very important trade hub so "nothing personal".
