/domoticz/domoticz: error while loading shared libraries: libssl.so.1.0.0: cannot open shared object file: No such file or directory
In stretch, libssl is at version 1.1.0. Solution for me (64bit Debian Stretch):
1) Download https://packages.debian.org/jessie/amd64/libssl1.0.0/download
2) dpkg -i libssl1.0.0*
Partitioning Scheme for SSD
Better leave all read-only files on SSD and use hard disk for everything else
https://wiki.debian.org/ReadonlyRoot should clarify which parts of the filesystem tree can be read-only: moving /usr to read-only would be the most significant thing (greatest space required) I guess but you have to ensure it is remounted as required when doing apt-get install or remove. See that page for more info.