Is the MAOI necessary? For making Changa, for getting a longer experience and administration time and being able to dose repeatedly after shorter amounts of time - Yes.
Also take into account that the MAOI content of Caapi leaf is minimal, for real MAOI Changa you will want to do a full-spectrum/Manske tek with either Caapi or Rue.
As far as IPA is concerned, my favorite Changa guide recommends methanol or ethanol (#2 recommended for food safety) as Harmala alkaloids are very hard to dissolve in IPA, apparently.
How about you mix up a batch of 1:1, try a tiny dose and if it's too much, put the Changa in an alcohol and add some more leaves. You can always dilute, the opposite is not that hard.
Just consider that having the option to break through easily is a better option than not having that option.

Best of luck,
Changman MAO
In my country, the legal go-to psychoactive substance is ethanol. Sometimes my friends get wasted and tell the craziest stories about how they go out at night to harvest strange grasses in the light of the full moon. They claim to meet elves, white light and jaguars. These are their stories.
SMAOLK ZEBONG
Mon Ami, if you lose your inhibition we can take some extasy and DANCE!