Should I upgrade to an iPhone 7 Plus or an iPhone 8 Plus?

Okay so I've spent a long time researching the similarities and differences between the iPhone 7 and 8 plus. The thing is… I can't decide which one I want. See, the price for the 8 plus is $799 which is a bit expensive but I can afford it. And the iPhone 7 Plus is $669 which is definitely good for me. However if I were to pay $799 for the 8 plus, I'd only get 64GB. And if I wanted 256GB I'd have to pay $949 which is outrageously expensive. But if I were to get the iPhone 7 Plus, id pay $669 for only 32GB but if I paid $769, I'd get 128GB. So I'm wondering which phone should I buy? And which amount of storage should I get? I have the iPhone 6 and every video and article I've read and seen, they recommend upgrading to the iPhone 8. But $799 is a bit expensive and I'm trying to avoid it, but if there's no way, then I'll pay for it. I'm one of those people who enjoys taking photos and downloads a lot of music. I don't have that many apps but I do spend a lot of time watching YouTube videos and going on social media. So what phone would you recommend?

IPhone x or iPhone 8 plus? - 1

Which is better and why? I currently have the 6 plus (had it since it came out) and it's time for a new phone.
~Thanks in advance

Constructing my own IPhone 6?

So firstly, is creating a phone a good option and if so, is it cheaper? (i don't mind how long it takes to create the phone either).
Also, what parts and tools would i need to make one.

I saw this guy do it on YT from China but i aint going there (Amazon will do)!

ICloud Activation Lock?

I recently bought an iPhone for my little sister off of ebay and when I tried setting it up for her it said that the phone had an iCloud Activation Lock. I don't know and can't contact the previous owner so I can't get their apple ID to sign in so I can unlock the device. What do i do?