Warnings about cryptsetup on new Ubuntu 17.10 installation?
Solution 1:
The first warning is due to conflicting settings in packages overlayroot and cryptsetup. (CRYPTSETUP is set by a hook, /usr/share/initramfs-tools/conf-hooks.d/overlayroot, that's why you did not find it in initramfs.conf.) I have opened a bug on this issue. Don't worry about it, it is purely cosmetic.
The second warning comes from the way the installer sets up swap space. If swapon -s shows that your swap space is active, then you can ignore it.