The foil (not sure it’s the right term - not a native English speaker 😇) is for the display. I usually just have a silicone bumper so the foil protects the display. Display cover might be the better term.

I don’t really use cloud services. There used to be apps that can manage access to several cloud services and even offer encryption like Cryptomator.

I am a bit sceptical about Mega because the guy behind it is/was on FBI radar so I would assume that they keep a closer look on his projects than any others. Proton as located in Switzerland is a better choice imo. On the other hand for non private data it doesen’t really matter.

I still use the brick from my 5s on my current 8 no idea about more powerful bricks.

Looks like you got the basics covered. You will most likely encounter several inconveniences- well at least I did when I switched to iOS several years ago. It is what it is - being in a walled garden. There are often less options to chose - where Android has 3-5 things how to do something on iOS there might just be 1-2. Ober the time I got over it though.

My only annoyances that persist are lack of sideloading (like from f-droid) and stupid/limited iTunes. There are however pretty good 3rd party tools that can replace iTunes like 3uTools (free) and IMazing (paid). I strongly suggest taking a look at then (IMazing has a feature limited free trial, so you can test before possibly wasting money). Instead of doing a full backup 3rd party tools allow you to just backup photos or contacts and also view/browse the data.