Your list looks pretty good

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A few comments:
- Provisional flight details for applicant's flight to UK (QUESTION: This flight date is earlier than the one I put on my application, just due to last minute changes. Will that be okay?)
Why not just do a new flight search for a different date and print that instead? It's only optional to include it anyway, so you can always just not send a flight itinerary at all.
For the finances, if you have them, I would also include the original job contract and the latest P60. The guidance states that UKVI can ask to see them if they want to, so we normally recommend including them if you can.
- Email Summary since we met (screenshot of inbox) - IS THIS TRUE?
Not sure what you mean by 'is this true?' It depends on the methods of communication you use as to whether it's true or not.
If you communicate by email, you should send no more than 2 pages showing a selection of emails send to each other over the period of time you have been emailing. Maybe one email per month, or one per week... depending on how much time you need to cover.
If you don't communicate by email, then you don't need to include any email inbox screenshots.
- Screenshots of Skype call logs going back as far as possible, one screenshot per mon - WE WHATS APP WAY MORE THAN SKYPE. IS THIS OKAY?
It's up to you what you send... you need to tailor your evidence based on how you communicate.
If you always Whatsapp, but never Skype, then include a couple of pages of Whatsapp call logs covering the length of time you've been calling each other.
If you never Whatsapp or Skype, but you send emails, then you send screenshots of your email inbox.
If you Whatsapp, Skype and email, then you send a couple of pages for each one.
I will make two copies of everything. Once again, thank you so so much! I am so grateful.
You only need to send 1 copy of any original documents you wish to be returned to you.
I would keep a copy of everything you are sending (especially the application forms) for yourself.