However, I personally hate any form of limiting people to playing what they want to play, when they want to play it.
Creating a direct rule limiting play styles, or implementing some kind of "mechanical fix" for this seems counter productive to the actual issue at hand, which is people making sure to keep the rules, and fairness of the server in mind.
I strongly agree with this sentiment.
Selling potions to allies of your main character for the purpose of helping your faction - that's just cheating. It's like making a rogue alt to spy on your main's enemies. Mechanically possible but cheating. DMs should simply mete out punishment.
Please do not increase weight of potions - Encumbrance is quite literally the WORST thing about NWN. There are a number of times when I've gotten so frustrated with encumbered characters that I have trouble enjoying them. I understand that it's immersion breaking to have characters running around with 20 sets of fullplate and 72 greatswords - But encumbrance is bad enough as is.