I see nothing in your post that requires FileMaker Server Advanced. FileMaker Server should be more than adequate for iPad clients using the free FM Go 12 app to connect as clients. And you might use some of the $$ saved to acquire FileMaker Pro Advanced instead of FileMaker Pro. This version offers a number of extremely valuable tools for development that can both save you a lot of time developing as well as be able to modify the user interface in ways not possible with FileMaker Pro.
But you would also do well to throuroughly research the technical specs and to evaluate your cell phone coverage/WiFi access available to your sales force before investing large amounts of $$ in your CRM. (And a sample CRM comes as a Starter Solution with FileMaker.) You might download the 30 day trial copy of FileMaker Pro, use it to host the starter solution and then try accessing it from an iPad using FM Go 12 in the locations where you would use your solution.
In areas where their is either poor coverage or a need for better response times, it is sometimes necessary to distribute physical copies of the data to the individual iPads for later "synching" back to the main database. This is typically accomplished with 3rd party produced Sync solutions such as those offered by 360 works and SeedCode.