Hi Dom,
We have implemented some massive complex campaigns, and never hit any issues with a limited number of steps. The main limitation is that the size of a canvas itself is restricted, and with a large and complex campaign trouble-shooting anything, or doing a sanity check can be like staring at spaghetti..
If you can split into more campaigns, it would ease building and testing, but if you want to report at the campaign level make sure you can report on everything you need.
Cheers,
Phil