Note that GUI tests are very fragile (= expensive to maintain), slow and it's difficult to find the cause if a test fails (because you usually test too many things at once and you don't know which one failed).
What I usually recommended in AX 2012 (when people insisted on automated GUI testing) was starting with semi-automated tests in Microsoft Test Manager (see Record and play back manual tests). You must define tests anyway before you can automate them and this allows your testers to run parts of tests almost immediately, before you have a solution for full automation. Test Runner doesn't work well with certain things like lookups, therefore getting everything fully automated would require some additional effort, but you surely can do it if you decide that full automation of UI tests makes sense in your situation.