Have you tried reading the thread? Someone already posted the same thing as you and got a response. There are some problems with the build that was released so they are re-uploading the builds.
What kind of request is this? The devs are not going to delete more syatem apps to make room for your apps. That's the stupidest request I've heard in my life. It sounds like you need to buy a new phone with more memory or delete some apps you don't use.
It's not in xiaomi.eu's hands what security update your phone has. Go complain in the xiaomi forums. Here: http://en.miui.com/forum.php?mod=forumdisplay&fid=92&mobile=2
Sounds like a you problem. No need to complain. Either choose your theme or use the dark mode (which was already reported to be INCOMPLETE in the first post!!)
Well, you do know the EU roms are essentially xiaomi's roms (but modified to remove crapware). So there really is no need to get sad about (nor look to complain about) something that isn't the Xiaomi EU teams fault.