I’ll break these questions down into bite size pieces as I have time for and allow others to jump in with answers / comments
Storing Data
Storing of info is easy, it really depends on how much you want to store, and there are a couple of was to go about it.
I am assuming you want an offline storage, rather than just a linking to a cloud/ server etc.
When you start talking about storing images, you are looking at something like the very SOON™ to be released Vivokey Apex , or the FlexDF2 / xDF2 / FlexDF
and this link should help
if you are talking about just text type files, something like the NExT Implant, xNT, FlexNT might do you, But if you also want Blinkies 
the an xSIID is what you will be after.
Check out TagWriter and NFC Tools to get an idea of what you can write to them…
HOWEVER
The problem here is, the chip design is intended for the easy transmission of information, so if there is a compatiable reader asking for info, your implant is designed to freely give up that info to whoever is asking.
You can protect the ability to write, but not the ability to read.
That being said, and especially is true of the smaller xSeries implants, the reader needs to be in VERY close Proximity to actually read the implant.
So it is highly unlikey that anybody could read that implant without you knowing about it, and even less so if you don’t tell people where to look and how to read it.
Obviously some stuff like passwords, SSN etc you could obfusciate
eg. simply by transposing a couple of characters