AFAIK right now, there is no limit, but in a hugely complex setup (lots of super and subcontrols, etc), I'm expecting some latency with 1000+ controls, but this is only for sending. Receiving should be unaffected.
In all cases 130 should be completely fine. But don't take my word for it! Mail your layout to yourself (so you can get it back). Then save a page, and then load it until you have 36 pages in MD (you can
create banks and pages) and see how everything works.
Note: if there is a memory issue, MIDI Designer will "dump" pages that it has in memory. This means that, when you switch pages, you'll see the "Loading" message and pages will be delayed. This is less likely in the iPad 2 and happens "like never" in the new iPad ("iPad 3").
Note: With the iPad ("iPad 1") you must kill all other apps while working with MIDI Designer.
While it is possible to get repeats of your Channels and CCs, you have to force that by not using "unused only." If you ever find that this is not the case, let me know and I'll launch a bug search-and-destroy mission.