There are many, many points/questions that can be made from this whole story, I don't even know where to begin.

First, there's no way that the entire story could have happened Bo Bayom (that day). The beit medrash mentioned in the story is in Yavne, and R' Yehoshua lived in Prikin (?), which was a few days away.

Second, I'm trying to remember the name of the sefer, I think it was Dorot Harishonim, that said pshat in R' Eliezer ben Azarya is that until that point, he was such a learner and delved so much into his learning, that the nes wasn't that his beard turned white, the nes was that until that point his beard was black (or whatever hair color he was)!

One of my questions on the story is why did R' Yehoshua change the moshul used when saying that R' Gamliel should be put back as the nasi? First he told the launderer the moshul about the clothing, and when he failed to get through the doors, R' Yehoshua came himself and gave a different moshul about the cohen. Why the need for two mashalot?

Just a little bit to get us started

In response to the Moshol question: He gave the washer-person a moshol that was fit for a washer-person. When he himself spoke to R' Elazar ben Azarya, he was trying to appease him by saying that kohanim have their jobs, Nesi'im have theirs.

As far as "Bo Bayom", can't it just mean the first day that the new policy was in effect?
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My questions:
1. What changed about R' Yehoshua's opinion? (or was he trying to avoid a confrontation?)
2. Because he didn't have a white beard!?!?
3. Was R' Gamliels policy of only admitting students who were "tocham K'varam" proper or improper? If it was improper, why did Heaven try to appease him?
4. 400 benches? 700 Benches? Whatupwitdat?
5. I remember learning, though I don't know if it's true, that R' Yehshua was the Av Beis Din. If it's true, why didn't R' Gamliel know about him earlier?