You may use all iPad models running iOS 11.0 or later. Due to the excellent FaceTime camera we recommend an iPad Pro. We suggest the cellular version as it makes you independent from unstable Wi-Fi networks.
16GB will be sufficient as the generated posts will be directly sent to the cloud. If you run offline campaigns and plan to send out your posts later, 16GB will be also enough.
This page compares all iPad models and provides you with further information regarding the resolution of the FaceTime cameras.