Burning means version 1.6.0 as the target for KR/NWO2 linkage.
1.5.0 is the next version which is simply an update for patch 1.03, along with major features in 1.5.1
I really didn't ever check this out but I'd guess this exactly is enough to run the game using both mods. Plus a couple of similar moves, like merging events.txt file. I don't remember if AAR makes extensive edits to ministers files, if so, merging those files would mean a little more fuss. However, I doubt that events would create any problem. In the mod's reference zip file, in "Event numbering.xlsx" you can find IDs used by NWO2. All are 7 digits long, beginning with 8, so it's not too easy to have any clashes.
AAR ids are 133[0]AA[Y]XX, so there is 8-9 digits. Thus, there is no overlap. 133 is the mod id. [0] is used as a buffer for now, but in the future, it will be used to designate which "submod" the event belongs to (Ex. AAR-KR linkage events, I used 1 here), [AA] is the group/country id (yes we have group ids), and XX is the event id (with an optional [Y] grouping number if >100 ids needed, this is mostly only used by me in CCIP)
Ex: 133011000 - An event for China.
EDIT: And I don't know about any AAR's additional UXX countries but I remain in hope that it doesn't reclaim any existing tags, just uses those few unused UXX ones. NWO2 doesn't use any UXX tags so there's little chance to have any problems here as well. (for the record: NWO2 will eventually use one spare tag for Free City of Trieste)
Aside from eventual KR linkage, we don't touch used UXX tags. We do use unused UXX ones, but that has been merged into the db for DH 1.03. For leaders/TT/ministers, they have all been merged into DH Full, so there isn't a need to merge that.
When I release 1.9.0 version, which I'm working on now, I may see if it's indeed that easy and post my observations. I had a cosy feeling that someone is eventually going to do this instead of me but the AAR+NWO linkup has seemingly never been done publicly so maybe it's time to do this properly
Burning and I would be interested. Let us know if you need anything done to make the process smoother. We do want to link to NWO2 for version 1.6.0.
As for KR, if you played the same Kaiserreich as I did, there's far too much ahistoricity there for NWO2 events and elections to make sense after 1945, IMO. Even if there are similar tags used for countries, I don't feel that strictly historical 1945 leaders hopping in into this alternative world would be right.
The current way I am planning to implement AAR-KR is a mass sleeping of existing events if KR history outcome happens, so no problems there.