Hi AC,
In my humble opinion, there is always "more than one way to skin a cat". The official guidance from SAP is to use BEx queries for the reasons that you can leverage existing BEx queries. However, I have found that the BEx queries that you have created for traditional BW reports do not work well with Dashboards. You better off create some brand new BEx queries that are optimized for dashboarding purpose.
Since you have to recreate the semantic layer for dashboarding anyway, it opens up other alternatives. It depends on what your skill set is. If you are very good with universe, you can easily put a UNX universe on top of a multiprovider. And then you can create all the variables, key figures, etc on the universe.
Either way, Query Browser is the way to go. Forget about Live Office as it will be sunset soon.
Hope this helps.
simon