What fun pictures!!! I also grow catnip and YES, it is very easy though I have never started from seed but from small plants - it grows quickly and multiplies like mad - returns every year en masse. You can easily dehydrate it in the microwave to use over the winter also!
Thanks for the pictures! Fun Fun!!!

PS - the plant stores often sell "Cat Mint" - this looks similar but is NOT the same thing - so read the labels
Nepeta Cataria is the one for cats
Nepeta Grandflora and Nepata glechoma are related