actually, I stumbled upon this: Moving an installation to a different drive and encrypting it with LUKS - a guide and it gave me a (crazy?) idea. I do not have enough experience to do fully manual install Arch style, but instead I can make initial unencrypted install (with separate /boot) using Calamares to get a working starting point, backup the root partition, create luks volume in place, copy the root back into encrypted volume, and then sort out fstab, mkinitcpio and grub.
call me desperate 
, but it should be quicker than full manual install, and i can still learn somthing along the way…