Largely independent of your size, 1mg Xanax will put you on your ass if you have never taken a benzo before and don't have a huge alcohol tolerance either (these things are cross-tolerant as they act on the same receptors). So with Lorazepam that would be 2mg as by this:
Code:
https://www.mdcalc.com/benzodiazepine-conversion-calculator
Antiemetics and acid reducers you can get from a pharmacy (if you can get them prescribed). In some countries they are OTC, worth checking. If not, sometimes you can pick them up on Ebay (i know i ordered them, but they didn't arrive yet, will update if they will).
To measure SN you would need a cheap jewelry scale, accurate 'nuff, you can pick one up for under $10.