I have been in the PNH program for about 8 years now. My recommendation for you getting back into the program would be to start with the "Success Series" videos, if you can't afford the whole set the first one I would choose would be the "Horsenality" video because it shows how each training session should be tailored to your horse individually. The next videos from the set I would go for would be: Seven Games, Safe Ride, Calm Ride, and Natural Rider; in that order.
To be totally honest I'm not a huge fan of the new Patterns videos and the new levels 1-4 videos are fine but my favourites are still the old level 1 in the red box and especially the old level 2 in the blue box. Sometimes you can still find them on ebay
. My very favourite Parelli video set ever(and I think I have seen them all) is the Liberty and Horse Behavior course in a box.
I hope that helps you decide where you can start. Welcome back to the journey!