Rob,
To answer your first question; you can input a Dwell in Fusion 360, but it won't act like you want it too. It will put an operation in your CAM Tree like any other operation, so it won't be placed inside the new operation tool change.
For Example: Adaptive Clearing --> 2D Contour A Simple Rough and Finish Tool path.
I can put the dwell in there and it will look like this: Manual NC (Dwell) --> Adaptive Clearing --> Manual NC (Dwell) -->2D Contour
Unfortunately, the dwell will be put before the tool change in each case.
You may be able to modify the Post Processor, you would just have to figure out where to put the G04 P#.
However, having a Dwell after the tool change would be a good idea to put in the Fusion360 Ideastation. I know there is a large number of hobbyist who use Fusion 360 who don't have ATCs on there machines. Having an option to wait on the spindle to speed up would be a nice feature.
Even though this will not work, in my opinion it is always good to learn something new. So have a look at the options you have in this Manual NC. Under the Setup Tab in CAM there is the option, Manual NC. Most of these don't do anything with Mach4 but some do, and they have come in handy before.
I also recomend checking out John Saunders Youtube channel, he has some great Fusion 360 videos. This particular video shows how he uses Manual NC and how to enable it.
https://www.youtube.com/watch?v=RqfZFBxvr-s