I think you are projecting your own thoughts on the text a little bit too far. Jacob wants to correct a wrong assumption about arabs and JEWS praying to the south.
2/ South from Syria, ("So from all this it is clear that it is not to the south that the Jews and Mahgraye here in the regions of Syria pray") but what part? Jordan?
3/ What is curious is to talk about the Jews, he talks as well of the Mahgraye to say that both pray to the East :
The Jews who live in Egypt, as likewise the Mahgraye there, as I saw with my own eyes and will now set out for you, prayed to the east, and still do, both peoples - the Jews towards Jerusalem, and the Mahgraye towards the Ka'ba
In Egypt then, all pray to the East (Jews, Christians, Mahgraye).
Then the question is why he is talking of the Mahgraye whereas he starts like this :"For it is not to the south that the Jews pray (sagdin); nor for that matter do the Mahgraye." What's the point to talk of them?
He then quotes different geographical locations by name to show that arabs and JEWS, wherever they are geographically speaking, pray to a specific location for each group. This is his main argument, nothing to do with praying east or professing Jesus.
Jacob associates the Jews and the Mahgraye praying always in the same direction wherever
they are, but to a place with different names Kaba and Jerusalem as if it was finally the same place. Is it? I don't know. And frankly I do not care because I do not need Jacob to know that at that time Kaba does not exist especially for Christians and without doubt for Mahgraye themselves... Jacob (d.708) talks about Kaba as if all ( and especially him) knew what it was and where it was at his time. Nobody knew before 708 what is was and where it was, whereas all knew where was Jerusalem. All. Moreover he is not able to give a place for Kaba.
Given the fact Jacob quotes other geographical locations , the only explanation is that this place is known to his reader. Like I said, we should investigate what was known as the patriarcal place of the arabs at that time.
1/ Nope, not necessarily. He does not give any place to Kaba, whereas everybody knows where is Jerusalem... and I repeat : Jacob associates the Jews and the Mahgraye praying always in the same direction
wherever they are, but to a place with different names Kaba and Jerusalem as if it was finally the same place. Is it? I don't know.
2/ You have some contemporary texts which give a place which seems to be Iraq. Academia is you friend for this.