I heard of someone a while back that had attempted to replicate something similar to 69Ron's SWIM's work with calamus.
20g calamus was shredded and washed in 400ml acetone for 6 hours, the acetone was filtered and discarded, and the mush was allowed to dry thoroughly. The washed and dried mush was added to 400ml distilled, room temperature water and soaked overnight, filtered and discarded to produce approx 400ml of tea. The tea was then divided into two halfpint mason jars. To find the active dose and test for allergies and side effects, the plan was to ingest 1/3 of one jar at one sitting, then the second test would be the rest of the first jar (2/3), then the third test would be the entire second jar (3/3).
The first attempt had no effects, but also no side effects. At the time of the second dose, further reading showed that Ron's SWIM had gone much stronger with additional calamus, and it was decided in the moment that the amount remaining would be perfectly reasonable, so down the hatch it went. At worst there was a mild stomachache that was easily remedied with a small snack, at best there was a pleasant relaxation for a few hours. Hard to say how accurate the notes are, but theoretically then, that last dose was a tea of approx 17g calamus washed with an excess of (maybe too much?) acetone and then extracted with water. No psychedelic effects of any kind were perceived, and as far as I know no further attempts were made, but I will keep my eyes and ears open.
To respond to your questions;
1. I would think fresh is better but I could be wrong. basically it's "old tea". Oxidation could reduce the effects, but could also catalyze them I suppose.
2. Everyone is different, so it is always wiser to start slow and move up, and in doing so titrate your own tolerance, rather than making wholly uneducated guesses.
3. No idea about powdered extracts or other methods of ingestion. Try it and report back?
4. The active chemicals seem to be a point of contention last I checked, hard to say exactly what you would be looking to purify. but as you say you are well-equipped, proceed with caution and please share whatever useful knowledge you can derive.
Good luck! Sorry I couldn't be of more help than that.