I don't want to see options on top of options for this feature. Make it work well all the time.
Well, then I would support gold weight >0. Not because stealing large amounts of money is bad and player should be restricted, but because it should be more noticeable when you are losing big bag of gold. Judging by my random checks, 0.01 is pretty good number overall. If you want to allow stealing more than 200 then you need to adjust it. I'd leave it at 0.01.
The game checks the stack when you click on it, before you see the choose amount window. I'm not sure if the code can be arranged the other way around yet.
Well, it would have been a nice addition, but it's not all that important.
I seem to like number 3 solution better, along with removing the max chance totally.
Yes, that may also work.
If we take top starting thief, then with T = y + x + x * fPickPocketMod we will have ~50-60% chance against commoner with average agility and 7-10 sneak for picking light item (0-0.3). Raising our skills by the same amount we raise NPC skills will only make our chances better, allowing us to try to steal items with more weight. Weight close to 2, however, will always be pretty hard: with 100 sneak, agility and luck we will have 39% advantage over NPC with the same stats, while item weight will adjust our chances from 0 to -50 with weight 2. If we want something more reliable at the start, then we can add iPickPocketMin * 5 to x. This way we will have 75-85% chance at the start and it will still be adjustable. However, if we increase our overall chance by 25%, we should lower our bonus on closing check, since 50% would be too much. I'd say it should be 25-35%.