If you want to go full on the Universal Century (UC) timeline, go for it.

But they are from the 70s, so don't expect top notch animation and scripts (it's a product of its time).

After that you can go Char's Counterattack and Gundam The Origin (this is a recent series, so more polished animation). Later maybe try watching Zeta.

As another comment mentioned you also some shorter UC side-stories like War in the Pocket, The 08th MS Team and Stardust Memory.