I have 64 GB of memory in my desktop with 16 GB of zswap. Can’t say I’ve noticed any difference because I haven’t actually been in a situation that uses all this memory yet (aside from some programs leaking memory), but the thought of getting “free” RAM is appealing to me.
It is possible to convert from ext4 to btrfs, but if you just installed the server it may be easier to just reinstall.