Thanks for the replies, although there's still some disagreement, even here!
Is anyone able to give definitive advice on costings, as the MS Licensing model has clearly caused some confusion - even with MS partners?
Does the E3 license make any difference here?
To clarify, while the app will be built and maintained by a single user, the Dataverse connection will be utilised to read and write data for all users.
Any further support if much appreciated.