S7 G930F International on Straight Talk AT&T

Hi,

I just received my unlocked G930F from B&H today (What a beautiful phone).
Exynos 8890 Octa-Core Chipset
According to "Phone Info" this was made on 2016.07.09 and assembled in Vietnam.
Product Code SM-G930FZKLTPA
Firmware code & Active code: TPA
Aavilable CSC codes: ALE, ARO, BVO, CHO, COO, EON, PCW, TPA, TTT, UPO, UYO
CSC Country: Panama
Mobile Operator: Home / 310410
I am located in New England.
The two Mobile Network types I have seen displayed so far under the SIM Card Status are; LTE and HSUPA

I did a manual update today and the current version is:
G930FXX1APG3/
G930FUUB1APEQ/
G930FXXU1APEQ

I have been trying to read as much about this version of the S7 as I can so I don't have to ask too many questions, I do have a few at this time though. My S4 was also on Straight Talk and would not update past 4.2.2 I needed a more reliable phone so now have this S7. I want to get all the security updates as well as any of the Android updates as they become available. Straight Talk is not so good about sending updates and I understand AT&T drags their feet on update certifications. Also, it appears some countries are more likely to get updates than others. I understand the UK gets frequent updates, I am not so sure about Panama.

I've read inserting a SIM from another GSM carrier such as T-Mobile even if not activated will allow updates via wi-fi; does this work to get the newest updates?

I want to keep the stock Samsung firmware for the moment & with that, is updating from the phone my best bet or is there a better way to get the latest updates?

Is there any benefit to having the CSC country reflect say, the UK or the EU as opposed to Panama? If so, is there a reasonable way to accomplish this & could you provide a link for me to look into it?

That's it for the moment, I have more reading to do... ;)

Thanks!