I don't think there is a limit on the number of processes & forms to be used within an application.
However there is recommendation for not having more than 20 variable in a single process.
Each process created within you application will become a service. So it doesn't matter having 500 processes in one application or 50 processes in 10 applications. You will endup with 500 services deployed into Java Runtime.
Forms also doesn't bother about the count as it just stay within repository (not in Java Runtime).
The only issue with enormous resources within an application is the response time to Deploy to application server (which you already mentioned here).
So, if you can split your resources into manageable units, that will reduce your checkin/deploy time.
The big problem I see with too many activities in a single process is that the editor starts flaking out, i.e., doesn't snap to grid, won't release when left mouse is released ...
Well, I faced the same issue several times. I noticed that this happens exactly when I use mouse pointer to click on any dialogs (say Checkout confirmation dialog); Instead If I use keyboard key(enter key), it's not happening.