Okay, thinking it over and over again despite what I think is insufficient evidence:
Who pushed Hoban? Anshu
Only one who actually had a fight with Hoban; Chef was suspicious but really had no given reason and Linae seemed to want to keep away from Hoban rather than get close enough to push.
When did he fall? 6:00
Two people saw him at 5:00. The Chef talked to him and found out that he was moody 'cause Linae was accusing him of being bad luck, which is corroborated by what Hoban told the Weapons master. Anshu said he spoke to the Chef at 5 and the Chef didn't know what was bugging Hoban. Due to the way info is coming to this, I cannot justify possibilities like the Chef finding out just after talking to Anshu.
Where on the ship did he fall? aftdeck
This is most difficult for me. But the aftdeck is close to the helm which is where the navigator should usually be. It's also a raised portion and more likely to have a porthole. Linae also saw him here most of the time from what I can tell. Finally, it's the last named location I can find him cited (albeit that's Anshu's story; Chef's story doesn't actually name where Hoban told him about Linae)
Where is Hoban now? G19
Two reasons: first, it's the odd X out. Second, it's the SIXTH mark on the chart! IF the marks are spaced hourly and the CIRCLE is 1:00, the odd X would be 6:00
Do you like Hoban's hat? yes
Well, this one's not a difficult one, now is it?
Question is, is Hoban REALLY still at whichever coord he fell over? WEEKS later? He's either used his navigational skills to best judge where to swim to hanging onto flotsam or he's loooonnng dead.
Guess we'll find out... this is as close as I can get to any coherent answer, though.