Hello and welcome to iMore! There’s nothing wrong with the 64 but if you can’t afford it it’s always best to go with the higher amount and I would go with the 128 if it all possible.
It depends on what you are going to use it for. If you play a lot of games, for instance, or want to download a great number of songs, you would be better off with the higher 128 GB or more.
Both are the same iPad, but 128 GB model has the twice the storage capacity of the 64 GB model. With that being said, you need to decide whether or not 64 GBs of storage space is enough for your needs.