Pitch is very easy to calculate, for most application 1/8th of an inch per foot is sufficient, but a 1/4" is "code". Just measure the section you are working on, say a 2 foot section and 1 foot off the ceiling to the center of the pipe, the high side will be 12 inches, the low side will be 12 1/2 if you used a 1/4 inch per foot. Just make sure you can measure off something that is fairly plumb/straight so it wont screw you. You never want too much pitch on anything, it may look like its going to do good but you'll find that things will get left behind unless theres a constant flow. So dropping with fittings like 45's or 22.5's isnt ideal even though it may look it. Less is more with pitch especially seeing you are running on a timer (I think???) so there wont be flow 100% of the time, if it isnt on a timer you should be fine but if not anything besides fluid will dry up and get stuck to the pipe causing buildup when dropping fast with the above fittings.
Also, when you use a level say you are using a 9" torpedo level, where ever the bubble is, say it takes a 1/4 inch of lifting one side of it to make the bubble center up, that means you are running a 1/4" per 9", if you are using a 2 foot level, you would have a 1/4 inch per 2 feet, pretty easy stuff.
Sorry just FYI, you probably know this but someone else may not.
I wish you good luck man, I love this setup and some time probably not too soon but I will do something like this. You definitely got my wheels spinning with that setup....thank you.