This functional canon is indicative of Mozart's utility writing, intended for domestic or pedagogical performance. It relies on tight motivic development that requires acute listening.
The challenge lies in balancing the voices so that the theme is equally identifiable in every entry.
Canon for 4 insrtruments is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 4.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Canon for 4 insrtruments lasts about 2 minutes.
Canon for 4 insrtruments is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.