Everything must be watch in the order of release for maximum enjoyment. ( and twists )
When i said that everything is not in order i mean regarding the second season. For exemple , the events of neko monogatari ( white ) , i mean tsubasa tiger happens during the time frame where araragi tell the events of shinobu time.
You see shinobu time take place after but feature araragi that tell events that happens earlier.
In the same sense , the events of "Mayoi Jiangshi" happens before tsubasa tiger in the chronological sense , yet are much more intresting to watch as intended , in the messed-up order.
After hitagi end , there is Suruga Devil , and that one happens much later in the timeline and need to be watched as it contain info regarding certains info of hitagi end
Anyway ,
what you should remember is:
-Watch everything in release order
-Pay attention to the date , for the event that happens in each arc , it give a much more intresting perspective to the events.Especially regarding everyone motivations.
Why do i say this ? because most of the conclusion/question and expectations you just wrote about this arc are actually adressed in the next ones.
For more questions don't hesitate to ask.
You need to watch suruga devil after hitagi end.
You need to.