Syrian Rue is not toxic at dosages used. I've used up to 10 grams of seed before, didn't notice any toxic effects, though i did notice some tremoring and body trembling along with a heavy heavy body load, but if you stick to the recommended dosages of say 3 to 4 grams of Rue seed, you'll be absolutely fine. The only thing about Rue is that pregnant women shouldn't take it because certain alkaloids in Rue can induce an abortion/miscarriage, but it's not toxic. I think anything above 10 grams isn't necessary and is just asking for trouble, not necessarily gonna be toxic, but definitely don't need more than 10 grams imo/ime.
Also as far as MAO-B inhibition from larger dosages goes, i've taken large/heavy dosages of Rue seed and extracts pretty regularly since 2012, even daily for 8 months, didn't notice any dietary interactions. Like i said, so long as you don't go over 10 grams or so, you should be absolutely fine.
Also Rue/Harmalas have a reverse tolerance, so the more they're consumed regularly (like a few times a week, to daily) the dose will get stronger each time and once it's gotten a bit too strong you can back the dosage down a little bit and continue on, then back the dosage down a bit more when it gets too strong again, continue on, and so on. Eventually you'll only need a little bit of Rue or Harmalas for a full dose, and in doing so, cleans up how the Rue seed feels because the Harmala content is stronger but the other compounds in the seed are in lower amounts with the reverse tolerance so it feels cleaner. Also the reverse tolerance cleans up the side-effect profile, does away with the nausea/vomiting/diarrhea and cleans up the body load as well as the motor function impairment and things just feel better and more tolerable.