How to deal with a lot of questions before switching to HTTPS?

Question

Information Security

Thinking about moving the site from http to https. I read a little. Lots of open questions for me. I will study the question, but in the hope of quick answers, I turn to you. If you know the answers to any of the following questions, I'd be happy to read them. I understand the situation, there are a lot of questions, but still ...

question 1 is
https slower than http? If the answer is yes, then what exactly is the difference in speed? Let's say that the page weighs 1 MB and is loaded via http in one second. Everywhere they write that https is slower than http.
Two sites ( one , two ) and conflicting information is given, perhaps because of my English.
On the first test, the test results show a slight slowdown in the site with https, and on the second, on the contrary, a significant advantage of https in a real test in speed over http.

question 2
Is encrypted content cached on the user's device?

question 3
Will an SEO link placed on another site via http work?

question 4
Do I need a permanent IP address?

question 5
Can a working certificate fail before its expiration date and the browser will display a message that the site is not secure?

question 6
Who are all these organizations (certification centers) that issue certificates, on what grounds, by some law or just like that, did they want to and issue them on trust, to whom are they responsible?

question 7
On what basis should you choose a certification authority?

question 8
I saw on some popular site different colors of the same castle, one yellow, the second green. What is the difference between them?

question 9
On some sites of these centers it is written about a guarantee of 5, 10, 100 thousand, etc. What does this mean?

question 10
What types of encryption do certain certificates have and which one should I choose?

question 11
Let's say that there are two certificates from two different certificate authorities. One ends on August 10, and the second is formed on August 5. Is it possible to safely replace one certificate with another without any consequences?

question 12
Is it possible to move with the same certificate to another server with a different configuration?

question 13
Will any certificate support all devices or does it depend on the certificate authority or certificate type?

question 14
What will happen to the display and operation of the site if this certificate is not supported by it?

question 15
Are there any differences between a paid certificate and a free certificate for one domain?

How many times I used an electronic signature, the same number of times it seemed to me that they were given out at very strange prices, and everything was done in a few minutes.