All iPad models have broadly the same core capabilities. Models essentially differ in their ultimate performance and physical attributes. iPad Pro models use FaceID for biometric user-authentication, while others use TouchID.
You can compare iPad models here:
iPad - Compare Models - Apple
The iPad10 is the current entry-level iPad. The iPads Pro M4 are the opposite end of the scale - top of the range, with cutting edge capabilities and hardware. Between these two extremes is the iPad Air M2, this model offering a mid-range high performance option. The iPad mini6 is perhaps an entirely different proposition - offering a smaller form factor and other differences in hardware and ultimate capability.
All current models of iPad support Apple Pencil; the Pro M4 and Air M2 models support the new Apple Pencil Pro and the low cost USB-C Pencil. Ensure that you choose the correct Apple Pencil for your chosen iPad - as they are not interchangeable. Also note that the Pencils also differ in feature support. Here is the definitive compatibility list:
Apple Pencil compatibility - Apple Support
Select Apple Pencil - Apple
Also perhaps consider that the iPad Pro M4 model are the only iPads to use the new OLED XDR display technology. This display is also the most power-efficient and offers greatest contrast and brightness of any model iPad - and also includes reference modes for professional colour grading. Also note that the current iPad Pro models with 1TB/2TB storage options have 16GB RAM, whereas the others have 8GB RAM; all models of iPad Air M2 have 8GB RAM.
All current models of iPad support iPadOS 18 - although upgrade to iPadOS 18 for the iPad Pro M4 models has been temporarily suspended pending fix of an issue with this model when updated from iPadOS 17 to the initial production release of iPadOS 18. This temporary halt to updating the Pro M4 is anticipated to be resolved in coming days.
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 make definitive recommendations for your personal needs, objectively I would council against purchase of any iPad with any less than 256GB storage, 512GB and higher having a greater margin for growth.
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. WiFi Only models of iPad have no GNSS/GPS capabilities with which iPad Location Services can derive location. This fundamental difference may significantly impact your ability to use mapping or other Apps that require precise location data - in particular if real-time positioning (e.g., a moving map) is required.
WiFi Only iPad models can only “infer” their location from a database lookup of neighbouring WiFi networks for which the geographic location is known, or the geographic location of your public IP address. For static applications in urban locations, where the location of IP public IP addresses and WiFi networks are known, an “inferred” location can be relatively accurate. However, in rural locations, or when using a Cellular/Satellite/VPN connection, location accuracy of an inferred location [if it works at all] may be very inaccurate.
Choosing a cellular model does not commit you to adding a cellular service plan for the iPad, but ensures that you have immediate access to GPS/GNSS and precision positioning services.
Returning to your question as to relative merits of iPad Pro versus iPad Air, only you can decide based upon your current and future needs. That said, you are now hopefully better able to make an objective choice between there or other recent models of iPad.
