iPad RAM

While this parameter has importance, Apple doesn't tend to highlight the RAM configuration of its iPad and iPhone models.

In very simplistic terms, RAM represents "fast" storage within which active processes are loaded - and Apps execute - whereas "storage" is much slower but more plentiful.

Apps and data are actively "swapped" into slower storage when the RAM memory is required by another process.

iPadOS is designed to use all of its available RAM so as to provide optimum performance; the more RAM that the system has, the less "swapping" is required - leading to improved performance and capabilities.

The iPad Air5 and current models of iPad Pro have 8GB RAM - while the 1TB/2TB models of iPad Pro have 16GB RAM. The iPad10 has 4GB RAM; other models may have the same or less.

In summary, the highest performing models of iPad have significantly more RAM than lesser models. For Apps that place significant demands upon the iPad system hardware, more RAM will be beneficial.

Whichever iPad model you choose, you would be well advised to purchase as much internal storage as your budget might reasonably allow - as internal storage (and other hardware) cannot be changed, upgraded or extended. The available internal storage is fixed for the entire life of the device. If you run out of internal storage for your documents, photos and other data, you will forever struggle and become a source of frustration. It is far better to have more storage than you need, than to need more storage than you have.

A good rule of thumb is to quantify how much data storage you will need - add a healthy margin - then double it. If you are unable to quantify your data storage needs, it becomes more difficult. Whilst I and others cannot cannot make definitive recommendations for your personal needs, objectively I would council against purchase of any iPad with any less than 256GB storage.

Within the Apple Support Communities we see regular tales of woe and disappointment when storage requirements are exceeded, necessitating replacement of the device; by contrast, we never see complaint of having too much available storage. It is relatively easy to fill limited internal storage space; perhaps consider higher tiers of storage as providing room for growth as your needs develop or mature - potentially extending the useful usable life of the device. 

Also consider the functional differences between WiFi Only and WiFi+Cellular models of iPad. Aside from the obvious Cellular functionality, only WiFi+Cellular models include GNSS/GPS location capabilities - which may impact any Apps or features that require accurate and consistent location data, such as Mapping. 

Purchase of a WiFi+Cellular model provides access to precise location services, but does not commit you to using Cellular connections. WiFi Only models of iPad have no Cellular or GNSS/GPS functions at all.