Welcome to the forum

.
To answer your questions:
1) No, it won't affect her case in the slightest. When she returned to live in the US, her previous spousal visa essentially became invalid, so now all you're doing is simply starting afresh with a new spousal visa.
2) Nope. A council tax bill is not required. All you need to do is provide your Land Registry document and latest mortgage statement (if you have a mortgage) to prove you own the property. I assume the friend is only living there while you are in the US? If so, I don't believe you need to include anything from him, because he will not be living there after the visa has been granted... i.e. UKVI will have no idea he is even there now.
3) Nope. Not at all.
So, all in all, your case is simple and not complicated at all.
The only thing that will make it non-straightforward is her previous visa refusal in 2015, but since she was successfully granted a spousal visa after that, it shouldn't be a problem.
In regards to your documents, my list is out of date now, because the application process has changed in the last few months, so I would list all of your documents anyway. For example, there is no Appendix 2 form anymore, as it has been incorporated into the online application and all your documents are now uploaded instead of being mailed.
For the relationship documents, you only need 2 photos of you together at most (usually we say one from early in the relationship and one recent) and you don't need texts/emails from the whole 5 years or 8 years, you only provide them for the time you were living apart.
So:
- If you lived apart between 2012 and 2015, you provide emails/texts for those 3 years.
- If you then lived together in the UK between November 2015 and August 2018, you provide evidence of living together for those 3 years
- If you lived apart between August 2018 and August 2019, you provide emails/texts from that 1 year
- If you have been living together since August 2019, you provide evidence of living together for the last few months.
So, that's approximately 4 years of evidence of living together and 4 years of evidence of communicating regularly while living apart.