Any less developed country that gets nuclear weapons is only thinking about the advantage it gives them. To expect less than that from Iran is just silly. However, there is only so long that the developed countries are going to be able to bar the less so from having the same advantages they have.
Yes, Iran would indiscriminately use nuclear weapons, because Iran has made many threats in the past. There are strong religious opinions in Iran, and there would be a large risk that Iran would hurt other nations with the weapons. Iran would have to constantly be monitored, and it would pose an ongoing risk for the rest of the world.
"Yes, it probably would use weapons without thinking but so would many other countries." - This implies that the "many other countries" are all suicidal. No competent state would use weapons without thinking, because they have to consider the consequences for their country. I believe that Iran would not fire nukes, for the same reason that the USA and Russia didn't. If Iran crushed Isreal, it would be leveled by the US. While they would be a considerable ongoing threat, and no doubt would wave their nukes around like lunatics for diplomatic supremity, I believe that Iran would not indiscriminately use its nukes.