Most of the time : yes.
Lands usually have no color, they are colorless, since they have no mana cost Lands usually have no color, they are colorless, since they have no mana cost
red
Black Lotus is an artifact with 0 casting cost. It has tap, sacrifice: add three mana of any color to your mana pool
wish counters make you pay a certain amount of mana to reaveal the top card off your deck you may then play that card without paying its mana cost.
'Casting a creature spell' means to pay the mana cost and put the creature spell on the stack. If this is allowed to resolve, then the creature enters the Battlefield.
While there is no "this card will win any game of Magic: the Gathering" card in print, there are those cards that are dubbed the "Power 9" The power of these cards are determined by the ratio of mana cost, energy used to cast the spells in the game, and effect. The strongest of these is Black Lotus which provides 3 mana of any one color, of the five colors of mana, for zero mana investment. Another powerful card is Ancestral Recall which has a mana cost of 1(blue mana) and the effect of drawing 3 cards. Other cards are a bit more abstract in their cost:effect ratio. Force of Will is a good example, it is a counter-spell with a cost of 3 generic mana and 2 blue mana which is very weak, but has an alternate cost of exiling a blue card and paying one life point which allows it to be played even when all your energy has been expelled casting different spell cards. While I have explained a lot in this short paragraph, I still have not even scratched the surface of the complexity and depth of Magic: the Gathering. The best way to test a card for strength is to play it in a deck, and see what it can do.
You pay X colourless mana, where X is the converted mana cost of the target spell. Converted mana cost is just a number, it doesn't take into account the colours it is counting. So if you were trying to negate Lightning Bolt, the converted mana cost is '1', meaning you would pay 1 Blue and 1 colourless for a Spell Blast targeting it.
X will be 0 in most cases, depends on the effect. If it's looking at the amount of mana paid to cast it, then it will be 0 if it is being brought back to the battlefield from the graveyard, it only counted as a value when the mana cost was paid for the initial cast.
If the sacrifice is a cost, then no. That'd be like paying one mana, and claiming it can be used for two different one mana abilities. Each cost needs its own payment. Sometimes an effect triggers when something is sacrificed. In that case, one sacrifice will trigger all of them.
No, lands do not go on the stack, cannot be countered and do not count as spells in any way.
Mana is magic. To get mana you need to collect 10 falling stars to create a mana star. Mana is used for magic items such as a flower of fire.
There is no hard limit. You can use a 100% artifact deck if you wish. It might not necessarily be viable depending on format, but there are some artifact land, and some 0-cost artifacts that produce mana.