+1 for M_B's entire post, listen to that fella, he knows his shit.
Regarding taking alpraze and codeine, I would advice to not take them concurrently! At least for the first couple of times of dosing codeine!
Secondly - antihistamines - I'd suggest Phenergen (promethazine being the drug name). But this is generally personal choice. When I was dosing I would use it since it has the added benefit of being a mild sedative (for some).
Thirdly, I'd doubt at those doses you'll feel nausea! At least nothing a little lie down for 5mins wouldn't fix. If you do want to cover all bases and have an antiemetic at the ready - don't even bother with metoclopramide (Maxalon)! It's absolutely useless, for any suggested indications! -_- lol
And finally, on the topic of filtering, you basically want to filter as much unwanted product (in this case, paracetamol) as much as you're physically possible!
But tbh to what degree is up to you! Some people just filter through a shirt - just enough to remove the larger particles. Some people like to do that, multiple times, then filter through a coffee filter (multiple times?) and if you
really want to be sure almost all of the paracetamol is removed, you could filter the solution again through micro filters!
If you're after advice, you'd be pretty safe if you're filtering through a cloth (to remove the large particles) and then a coffee filter once or twice! The remain paracetamol would be equal to, or less then, what one would consume taking them as per the directions.