furkan Which one is best for cache selection? can I use multiple caches?(fastcli&redis or redis &memcached)
I'd use only REDIS, nothing else.
Is Let's Encrypt suitable for e-commerce? Do I have a problem if I use Let's Encrypt?
Let's Encrypt should be fine. But it's not a silver bullet.
I'll upload files via contrat form 7. file format psd for print press so should file upload size 1gb or 2gb .. Does doing so affect adversely?
Be prepared to deal with timeouts. Such huge file sizes take a lot of time depending on how good or bad is your visitor's Internet.
I take a backup of my site. How do I back up?How do I move the old server to the new server in an easy way?
There are tutorials all over this forum. Please, use the search feature.
How do I create a site theme and install this theme on different servers. Can you do this with the worpdress plugin?
I'll leave this for someone else to reply.