Then just pick btrfs. 
Unlike Fedora, which takes a very aggressive stance on patents, we install the most common codecs by default. If you need something other than that, it should be pretty obvious because the media will fail to play.
If you want hardware accelerated playback of video there may be a little work to do. See here for the details.
There isn’t really a fixed list. If gaming is your priority, you could take a look at this guide.
You can use timeshift on EOS. I would recommend choosing grub in the installer to make timeshift rollbacks easier.
You probably won’t need many flatpaks here. The repos + AUR provide a pretty wide range of software.
If you choose the plasma desktop, we install haruna by default.