Looks alright to me. So long it has the lightning port it would be ok.There are many manufacturers that supplies cables for handphones. I for one would look out for those cables that comes with "MFI" certifications. MFI = Made for iPhones are those cables which have been tested by apple and certified safe to be used with iPhones. These are the cables you should be getting.

I am using the nylon braided Anker MFI cable. Its RM70 but very tough, durable and also faster charging. Then there is the Aukey braided cables these are also recommended. Price around RM55 and compliments their qualcomm fast chargers very well. Bought through Lazada.

There are ways to tell whether the refurbished models or not. If from Apple themselves, refurbished apple certified handphones have 1 year apple warranty. There is no such thing as Grade A or 3 stars etc etc, these are all local refurbished and some have warranty whereas some do not have but are reflective of the offer price.

Apple mentioned somewhere in their website that batteries should have a health of not less than 80% capacity after the 2nd year of ownership. So with your calculations above, it looks good.

Probably bakground apps are still working(downloading etc) after you put it to standby.

I was referring to those who are wanting to buy refurbish sets, however thank you for your clarification.