Preparing changa is easy. Check the Wiki or FAQ and there is a whole section on it. It even has a bunch of different herbs and their potential effects. Basically, dissolve your spice in a minimal amount of acetone, then evaporate that spice containing acetone onto you caapi leaf. Make a 1:1 ratio, it's the best and easiest to dose. In other words, 1 gram spice to 1 gram caapi leaf. Changa is awesome, but there are many other herbs that offer great effects too. I personally love Calea and Blue Lotus.
MAOI's with spice is a big step, but after you do it you will see it's a great way to go. The synergy between caapi or rue harmalas and spice is simply incredible. Yes it makes it last longer and more intense, but at the same time you will notice the harmalas lending you a helping hand during your journeys. Hard to explain until you experience it yourself.