There are two main reasons I've been using cloudflare behind a proxy
Really fast DNS updates. Sometimes I will allocate a forum to another server and not having a "up to" 48 hour update window is nice.
It also hides some ports like ssh, even though it doesn't seem to help cut down on logs much 
I'll share my experience in detail.
Actually I feel using CF for DNS is only good Choice Else a Myth.
TTFB Race ...
1Dot i have setup a cloudflare account, you mentioned earlier
1Dot You can still connect to terminal when you use cloudflare all you need to change NameServer and cloudflare doesn't even touches port 22
After changing all proxied, below in SRV there is still parts of my host server, for example:
Which one should we use in Target
HERA.NS.CLOUDFLARE.COM or JIM.NS.CLOUDFLARE.COM
is it really the one we should change for terminal to work?
Braden for terminal to work you should just use SSH and connect to the IP address instead of the hostname. That way, you won't expose your IP address.
1Dot this is incorrect. If you try to access SSH using the name of the domain (for example, ssh admin@nysite.com) and you are behind CF this will fail. It's because of the A record entry which CF will mask with one of its own IP addresses instead behind it's proxy.
The nature of TCP is that the connection request waits up to 30 seconds for an ACK response it will never receive, and so it times out as a result.
Braden you can use the local command prompt on Windows for this. Just just ssh myuser@ipaddress -p 22 (I'm assuming Windows - it'll work massively in Linux also from CLI and you won't need the port if you are using the default.
Braden Hello yes you can still do ssh but with IP I was incorrect I by mistake said as I always do it with IP, I have a best tip for you use mobaxterm portable free version here your ip will be saved once you login and also you will be able to see a visual file manager so easy work actually. 
Braden In File Size Optimization, did enable Auto minify?
Yes it's good here is the detail tutorial for flarum written by me also the main thing is edge cache just enable that for a month (Not tention when you will update css/js it will be automatically done as flarum adds ?version in file) only for assets folder.
wOW Flarum now is fast! 
And remaining
I have a question, why in page rule use only EDGE cache , what would happen if we add browser cache.. too?
Braden the browser cache default for CF is 4 hours. Your don't need the edge cache rule
Braden Just make sure that Brotli is enabled plus http2 (which should be by default)
Braden If you can access files then Cloudflare also can access and also 755 is recommended by flarum so its great.
1Dot He need it actually.
He really doesn't. But ok, if you insist.
but instead you'll have to use a SSH program, omg! I wonder which answers will 1Dot come with after reading this
at least they recognize if they thought we have been counting winds, We counting blessings! 