Understand that only WiFi+Cellular models of iPad have GNSS/GPS capabilities - this being a function of the iPad Cellular chipset. WiFi Only models of iPad have no GPS capabilities with which iPad Location Services can derive location. This fundamental difference may significantly impact your ability to use mapping Apps - 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.
This fundamental difference between iPad models has significant implications for non-static mapping applications. If you need to have moving maps, or have future flexibility to do so, you may need to consider a WiFi+Cellular model of iPad. 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 positioning services.
Both WiFi Only and WiFi+Cellular models of iPad can be augmented with an external dedicated GPS Receiver - connected via WiFi. For WiFi+Cellular models, using an external GPS receiver can beneficial, as the receiver can be positioned in an optimum location to avoid screening from obstructions from the fuselage and within the cockpit. Be mindful that the iPad will need good line-of-sight to provide a good 3D position fix (obstructions will result in reduced performance due to increased DOP).
External GPS receivers are commonly used in marine, aviation and vehicular applications - and can be either directly connected via Lightning or via Bluetooth. There are various third-party manufacturers, of which two are BadElf and Garmin GLO. For cockpit use, a GNS3000 is a popular and recommended choice.
As for differences between the 2024 iPads Air M2 and Pro M4 chipset, Apple does not provide specific information in this regard. If you wish to make this comparison, you may find that one of the popular "teardown" websites may provide additional information.