Re slavery, droids are decent at manual labour, it depends on what you use them for. Human pilots and soldiers appear to outperform droid armies on the whole, unless they are very high end. Anakin is a pilot and low grade mechanic at 9, he's pretty valuable. Shmi likely also has some relevant skill.

We don't really see slavery used as large scale manual labour very often. Per that Kaminoan in AOTC (admittedly while talking up his merch, creative thinking is the big advantage)