If I factory reset my phone, will it downgrade me to back to IOS 10.3?

Last weekend I decided that I wanted to upgrade my iPhone six plus to IOS 11 beta, and before I did so, I backed my IPhone up on Itunes. Now I want to downgrade back to IOS 10.3 since the actual update is coming out this week, however the computer I backed my IPhone up on is not functioning properly. I was wondering if I logged into my ITunes account on another computer, would my files be there, or if I just factory reset my phone alone will I downgrade back to IOS 10.3 and just have to deal with losing everything?

How to stop I message?

I just bought a samsung phone. I used to have an iPhone. I text me Dad ( he also has an iPhone) from my new Samsung and when he responded it was an iMessage that went to my ild iPhone using Wi-Fi. It did not come though on my samsung. I will no longer will be using my iPhone. How do I make it so when I text from my samsung the response will come back to it and not my iPhone via iMessage

Should I buy an iPhone 8 through Apple or Virgin? Also, how to transfer pictures?

I currently have an iPhone 5c and I'm going to buy the 8. My current carrier is Virgin and I will be staying with them when I get the 8. Should I preorder it through apple and then activate the phone or preorder it (when its available for preorder) through virgin? What are pros and cons on doing it either way?

Also, is there an external way to transfer photos from the 5c to the 8? I will be creating a new Apple ID when I get the 8 so things like my contacts won't transfer when I sign into my ID on the 8 because I will be creating a new one. I have a Mac, is there a way I can do it using the Mac? Like, if there was a cord that went from one iPhone to the other and transferred that would be great!