What's the difference between reactant, excess reactant and limited reactant in a balanced equation?
Suppose that you want to make a cake. You would first need to go your fridge to check whether you have the necessary ingredients to make one. So you go to your fridge. Luckily, you have all the ingredients: milk, eggs, flour, and frosting. So you decide to make one. You also decide to make the cake as big as possible to avoid the hassle of cleaning/preparing again. Now, what determines how big you can make the cake? 

It is the quantity of ingredients of course. But what happens if you  have enough milk to make a 10 cm cake, enough eggs to make a 1000 cm cake, enough flour to make a 1000 cm cake, and enough frosting to make a 10000 cm cake? How big can you make the cake? 

You would only be able to make a 10 cm cake. Because you would run out of milk. And since you no longer have milk, you cannot make anymore cake. 

Lets go back to your question of excess reagents and limiting reagents. The limiting reagent is the milk in the example above. It is what determines how much of a product you will obtain. It is what limits the amount of product you get (hence the apt name limiting reagent). Everything else are excess reagents: the eggs, the flour, the frosting. They are leftovers; they are in excess.

Now question 2. You cannot tell which reactant will be in excess by just looking at the balanced  equation. Going back to the cake example, the balanced equation is sort of like a recipe for the cake. You cannot tell whether you will have eggs, flour, and frosting left over by just looking at the recipe. You also have to check your fridge. In other words, you have to know what you are starting with. 

Now question 3. I think question 3 will be answered in more detail as you study more chemistry. A complete answer involves thermodynamics and statistical mechanics. Nevertheless, going back to the example of the cake: Whether or not you can make cake depends on whether you have all four ingredients. It also depends on how much of each ingredient you have. If you have no milk, you won't be able to make any cake.

But say that you want to make boiled eggs as well. You only need eggs to make boiled eggs so you would could turn all eggs leftover eggs from the cake into boiled eggs. The fact that you can make boiled eggs with the leftover eggs does not change the fact that you can make a 10 cm cake.  

This is what the two equations are trying to get at. The major product, will be determined by how much of a certain reactant you have. It doesn't mean that the reaction is solely determined by what it is in excess or not.