Great post, good info, good questions, good research.
Good idea.
The following is just my opinion, so take from it what you will but make your own decisions.
I will mostly buttet point fir readability and time saving, but there should be enough to get the…point
Before I start, my opinion would always be a Flex over an xSeries, but I see why you are wanting the xSeries.
FlexUG4, great option, the most flexible use implant there is.
AND if you have a Flipper, this is next level convenient
R1 great position for a work badge
The NExTv2, at first I wasnt sure why you would want one, but guessed and was confirmed when you said 
R0 perfect spot for a 2in1 implant
The LF also makes sense, or an xEM if you dont care about the blinkie…but it sounds like you do.
This one is Tricky to answer.
Outside of it being far more capable than NDEF storage, but that seems to be what ~95% of what people use it for.
The FlexSecure would be a better option, BUT you are also wasting capability for just NDEF
I agree though, It would make a great little storage implant.
P0 is a goid spot for it if you use it a lot, for me, I would use it as a data stash in a hidden implant position and save the P0 for something I woukd use more frequently or another 2in1 like the xMagic.
With a UG4, do you need a FlexM1?
Dont get me wrong, I have both, and I got the gen2 so I could write to it with my phone, and used it for hotels etc.
But that purpose became my FlexUG4, and my FlexM1 is now enrolled into a number of things so I dont really change the UID anymore, but I use it a lot…
OK
Ignore me, get both the FlexM1 and FlexUG4.
Also I remain a fan of the gen2, but I think the gen1 is more popular
More reading here
I have / had xBT in the armpit, great location, I had to use a Flipper, but ai always have one nearby so it was easy, The VK Thermal would be much easier with a phone, andcI imagine an RSP would certainly help getting a consistent read.
I will be getting one at some stage, so I can’t vouch for its accuracy just yet, but research telks me it is good.
More info
App link
I love my FlexSecure, have you considered one FlexSecure and an Apex?
A little outdated, as there have been dome major improvements since I posted this
Although I do see the appeal of 2 x FlexSecures also.
Some useful references
FlexSecure Practical Reference
Fantastic plan.
They can also be used as a backup after your testing.
Great investment
Thats totally up to you, and everybody will have there own opinion on that, Heres mine and what I woukd do.
If you’re going to pay a pro and baby your hand for a day or two and the healing itself takes about a month, you might as well get it all done in one shot.
When you break down to even just the time and money, doing it all at once is a no-brainer:
Healing Time:
If you are getting one implant or ten, for each implant, it takes about a month to heal. Do them together, you heal once over a month. Do them separately, you’re looking at nearlyba year of constant healing.
The Logistics:
Every single trip means commuting, fuel, parking, and taking time out of your day.
Multiply that by 10 if you do them individually.
The Piercer’s Setup:
For every session, the piercer has to do the paperwork, prep the station, and open up fresh, sterile supply packs (drapes, gauze, lube).[Also provided by DT but some like to use their own]
Because a single session saves them a ton of setup and material costs, they SHOULD pass those savings on to you with a discount for multiple implants.
In short:
Travel once, stabby-stabby, and you’re completely done!
Healing:
Depending on your job, you may want to take a couple of days or weeks off to baby you healing.
Cons:
Discomfort over multiple install sites might make “doing things” a little more difficult.
More shock and a strain on the body for healing.
Plan them out,
Take a photo of your hands (Or stock photos)
Photoshop / draw / AI your suggested implant positions
And post here for opinions if you want.
From what you have above, I think you have a great plan.
Also, Was “insanity” check rather than “sanity” check intentional?