Alas, with the Note 5 you GIVE UP both 1) User Replaceable Battery, and 2) "External Storage" (micro-SD card slot).
Those two factors - PERSONALLY - easily outweigh any Advantages the Note 5 may offer, and the Note 4 purchase was not made until the 5 was released.
As for Spare Batteries, have been very happy with the Anker kit purchased for a Note 2.
That kit came with 2 batteries + a wall charger, and all 3 units have performed well.
Recall seeing that Anker had batteries for the Note 4, and would not hesitate to purchase one when that seems appropriate (barring convincing reports that their Quality has fallen, of course!).
[The Note 2 remains in Daily Usage as a "PDA" - it still works Just Fine, and hope is that this continued usage will prolong the lifespan of the Note 4....]
This is a good point but it has to be a matter of personal preference. A few years ago I would have agreed that having expandable memory was a must - however, I have fibre broadband at home and unlimited mobile data so every photo or video I take gets uploaded to the cloud the day it gets shot. I'd have to do this (eventually) regardless of how much memory I had so for me it's easier to just do it every day.
As for the removable battery there's no denying this is a plus. However, again personally I'm never far from a power outlet and also have a 10000mah portable charger and this thing charges FAST. I guess there's also the issue of the battery degrading over time but in all honesty I don't keep phones longer than a year, although this Note 5 is so good I'm hoping to keep it much longer.