

I get LFTP and somewhat cron, but why OpenSSH? You can also SSH to the host and get into the container from there.
ITry to keep containers minimal, meaning only add what you absolutely need. Also I advise you to keep/consider the content of the container as immutable. If something’s wrong, throw it away and restart with aa clean container. Data that you download should reside on a volume mapped to the container and this can usually also be accessed from the host. Same for any LFTP/cron config, etc.
So, what exactly is you plan why you need to SSH into the container itself? This post smells a bit like a XY Problem.
A quick google reveals that there are ready to go docker images with LFTP (which weighs about 7.5MB), which might be completely suitable for your need depending on your use case? https://hub.docker.com/r/minidocks/lftp/
4/5 mit Reis(en)