I only know your name and 5 centimeters per second from him so far, should you know them all?
In the end, you do not have to do anything at all, but if you've already liked them, there's nothing wrong with seeing others.
Definitely not all know, he has three films that were good, no masterpieces but quite solid, have the remaining tested but was really 0 of it.
Outside of the two you mentioned, The Garden of Words (Kotonoha no Niwa) is also recommended, again, not a masterpiece but still pretty good ^^
It is not a must. But I think they are all worth seeing. ^^ Especially if you have already liked the two.
Above all, The Garden of Words is very nice to look at.
The trip to Agartha, however, more reminiscent of a Ghibli.
The Place Promised In Our Early Days and Voices of a Distant Star - guess if you liked 5 centimeters per second then it did.
There's also a short series of him: She and her Cat. It is told from the perspective of a cat. Very emotional and sad.