Just a heads up, serotonin out competes serotonergic psychedelics for the same receptors. So it's very very likely the SSRI is the reason you have been a heavy weight in the past. When you jump into taking psychedelics without SSRI in your system, just remember your head may not be as hard as you've come to believe it is. Start as if you are taking it for the first time with low to average doses and work up rather than taking for granted that you need heavy doses to get any reasonable effect.
You don't mention which MAOI you are planning to use, I'm going to assume harmalas.
For vaporizing/smoking, harmala/MAOI is not vital at all, they are a great addition, they extend and slow down the experience allowing one to work with the inhaled tryptamine more effectively, but not required to get an effect. For oral dosing they are vital, since the DMT will be metabolized before it can cross the blood brain barrier if MAO is not sufficiently inhibited.
For the changa, just load the whole batch up into a bowl and puff till it's gone (or till you are, whichever comes first). Long, slow hits, hold it in as long as you can.
For the freebase I'd say go ahead and orally or sublingually dose the harmalas and when you start feeling the effects from them vaporize the freebase as you normally would.
An average dose of sublingual harmalas seems to be about 20-40 mg for most people.
Oral dosing of harmalas is incredibly variable, some people will be on their backs at 100 mg and some people won't feel anything till 300 mg or more. I'd suggest doing some experimenting with oral harmalas alone to find your correct dose before you add DMT to the mix. The effects you are looking for are feeling very stoned and dreamy, you may experience some nausea and vertigo, especially your first few times.
Hope it helps and please let us know how it goes.