I have no experience with chacruna, but with caapi the long boiling times are optional. There is a theory that some THH alkaloid might be generated with long boils resulting in a qualitatively different experience, but for most part it's just about how to extract the alkaloids most efficiently.
I have done 3x30 minute boils with caapi. That is drain the water out of the plant material after the boil into a jug and then add more water to get more alkaloids out. You will get plenty with that 3x30 min boil. The more water you use, the more soluble the alkaloids will be, but the more you will have to drink, unless you reduce boil the resulting juice to a comfortable volume.
There's no reason you couldn't do a boil with 25 grams. Only reason to do big batch is to save time as far as I know. I believe 25 grams is a pretty good starter as a dose.
You will get some effects from the caapi alone but definitely not the full experience. For that you need the DMT containing plant such as chacruna. You can start carefully, by ingesting just little of the DMT on top of the caapi.
Nausea is something that can be learned to handle, but if you feel like cheating, you can buy lemon essential oil and encapsulate it for greatly reduced nausea.
Also, you should check the interactions between MAOIs such as the alkaloids contained in caapi and any medication / substances you take.
Best of luck and please report back on your experience!