a) "Arabs" can refer to either the language/culture or to the ethnicity originating on the Arabian peninsula. I gave you the benefit of the doubt as to not say something are stupid as "Jesus would look like someone who speaks Arabic", and assumed you were talking about the ethnicity, since language isn't a skin color.
I assume it is merely your ignorance to not know that the vast majority of "Israeli Arabs" are the Muslim/Christian Mandate Palestinians who happened to be on territory annexed by Israel after the borders were settled.
b) It's silly to pretend there is continuity in the population of that region. I'm sure there's lineage, no argument there, but that region was conquered repeatedly, destroyed in the conquests, abandoned by the empires for centuries only to have floods of immigration for a century (both Jewish and Muslim).
What on earth...? There is no "continuity" but there is "lineage"? You may as well argue a towel is soaked with water but is not wet.
There is precisely zero evidence of mass depopulation of Palestine at any point. Yeah, the odd city was sacked, there was war, there was disease, but never wholesale depopulation. One can point to immigration, particularly maybe late 19th / early 20th century, which can only be estimated. However, most of the more reliable estimates of pop growth would arrive at about 85-90% of the 1947 Arab population being natives.
It is however very political advantageous for Israel (and by extension the US right) to make a great deal of Arab immigration, because the task is fundamentally to deny that Palestinians have a moral right to the land they lived on and owned until 1947. So they're not really Palestinians. There aren't supposed to be real Palestinians with (as you put it) lineage, just a bunch of johnny-come-lately interlopers who implicitly should be kicked out ('back') to Jordan, Lebanon, Egypt, etc. And just in case we weren't clear on this, more rabid pro-Israeli supporters will also stress that they only turned up in the first place because the Jews were creating so much wealth and prosperity. Uh-huh. Even in the early 20th century, what was the Jewish claim? "A land without a people for a people without a land". They were rhetorically disinheriting the inhabitants long before the state of Israel even existed.
If we moved back to the basic thesis of what Jesus looked like, however, one might note that even the Jews of Jesus's time were themselves something of a mongrel race, Canaanites intermixing mostly with Syrians, Egyptians, Phoenicians and the various nomadic desert tribes we'd now call Bedouin, etc. If your central thesis is that the modern Palestinians won't look much like ancient Palestinians because they have intermixed a bit with Levantine and Egyptian immigrants despite the fact that the ancient Jews were themselves the products of intermixing of Levantine and Egyptian populations, your argument sucks.
c) They're genetically close relative to what?
Close
to each other, as is the obvious meaning of that sentence's construction. You seem to think the idea near-heretical, when in fact it should make perfect sense to anyone who hasn't swallowed the pro-Israeli propaganda that the Palestinians have nothing to do with the pre-Roman population.
Yes, Jesus would likely have looked like an average Israeli Jew. I would suggest a Palestinian ahead of an Israeli Jew because whilst the diaspora will have mostly interbred with Europeans, the Palestinians will have interbred mostly with their neighbours, and those neighbours will have looked more like the ancient Jews than Europeans. I am aware this is potentially a thin distinction, as I'm not sure people could tell many Israeli Jews from Palestinians by their facial features anyway.