In general, you drink the potion by double clicking on it, and thereby receive the effect of the potion. There are two exceptions to this:

If you double click on a poison potion, you will drink it. Although this is not inconsistent with the way other potions work, it is probably not the result that you intended. To use the poison on a weapon, you must use the poison skill from your skill list.

The explosion potion is also different from the others. When you double click on an explosion potion it is like pulling the pin on a hand grenade. You then have a few seconds to select a target for you potion before it explodes.

Since all player made potions are now identified all of the time, and since the other potions that you may come across are all of the same strength, the only use for the taste identification skill is in determining the contents of potion kegs.

There is much debate over the correct answer to this question, and the general alchemic community is divided on the issue. The official opinion of the alchemy guide is that the skill of the alchemist has no effect on the quality of the potion produced. (Note, that this seems to be at odds with both the general opinion of most alchemists as to how the skill should work, and with the original intention of the designers of the game)

Saying, "As little as possible" is probably not going to help you much. The truth is that there are a lot of things to consider. But they all involve getting what you pay for. Look over this list and decide if you are willing to pay more for them or not:

1. Convenient location (in/out of guard zone, easily accessible...)
2. Highly skilled alchemist
3. Well stocked (with the type and quantity of potions you use)
4. Alchemist who can answer your questions
5. Alchemist who is not a mule

The more of these things that are important to you (generally speaking) the more your potions will cost. The Potion Reference Chart gives a range of prices for each type of potion.

There are a few things that could be happening here:

1. You might be waiting too long to throw them (click on a target)
2. You might be targeting terrain that prohibits explosion potion.
3. Your lag might be bad enough that you don't have time to throw the potion
4. If your Paperdoll is on the screen, it seems to increase the lag for potions [this has been fixed]

The Potion Tactics section has more information about each of these possibilities and what you can do to minimize the effect of each.

The nightsight potion is not on a timer. Instead, its effect lasts until the dawn of the next UO day. Because of that, everyone loses their nightsight ability at the same time.

You can use potions with any one handed weapon (the UO Stratics Weapon's page lists which weapons require two hands to use).

Potions are further restricted in that you cannot use them when you have a shield equipped (though rumor has it that this restriction does not apply to explosion potions).

The only things that are stackable in the game are objects that are identical. The long version of that sentence goes like this:

In order for an item to stack, there can be no information that is stored about the item that can change from instance to instance. For this reason you can not stack armor and weapons even if they have the same graphics (because they have different internal information, like the type of magic they possess --if any) And even if you were talking about two weapons that were EXACTLY the same, as far as powers and abilities go, they still could not be made to stack because each COULD (it does not matter if they do or not) have a different amount of damage done to it.

This is the same reason that potions can not stack. Even potions of the same type (Healing --the yellow ones). Even potions of the same strength (Greater Healing). They still have some information that can be different between potions. Do we know what this information is? Not that I have heard from a reliable source, but we all have out opinions.