You can use as many seals on an artwork as you like. You might want a large seal for a large work of art or a small seal for a small work of art. Depending on the design you may need a seal with a light background or one with a dark background. You may need a round seal or one that is square, rectangular, or an irregular shape. You may decide that the piece requires more than one seal. As an artist you can never have too many seals. It is, though, quite possible to use too many on one work.
The painter of the ancient work illustrated above is not to blame for this profusion of seals, although it does make for an interesting composition. All of these seals have been added by later collectors who wanted to show that they had owned this famous artwork by attaching their seals.