I've set up a standard report and included conversions/floodlight activities. This report has everything we currently need. Why are you suggesting we create two reports and two data sets? Why can't we just use one report and add conversions/floodlight activities as needed?
In the past, if you've set up a standard report and added activities over time, you had to submit a ticket for those to be added to the data set. By utilizing two reports and two data sets, you don't have to rely on us to update your data set if new conversions/floodlight activities are added--getting you the data you need quicker.
When setting up Campaign Manager reports, please reference the following:
Because the dimensionality of the reports are exactly the same, except for activity and activity id, you will be able to blend these data sets within Tableau.
To learn more about configurations that are important in order for ChannelMix to pull your Campaign Manager report efficiently and accurately, check out this article: Google Campaign Manager | Configure Report for ChannelMix