Tahllas's page

Therefore at 20th level, an artificer can have one invention with five level-1, 2, 3, and 4 spells. it takes 200 hours to make (about 1 and 1/2 weeks non-stop) and it needs the use device skill after 11 uses and requires a DC45 use device for all of those spells used at once. any of those failing completely ruins the device.

They are not spell casters so they do not get the bonus.

The chart shows the number of spells in any number of inventions so the 3rd level artificer can have one invention with three spells but at the consequence of failing quicker or the artificer has 3 inventions of two 1st level and one 2nd level spell.