Is it possible to combine all five chakra elements? The title says it all... but I'll elaborate:


Initially we see techniques derived from a single chakra element (Katon, Doton, Suiton, Fuuton and Raiton). These are the most common, since usually a ninja can master only one chakra nature (since normally ninjas tend to have an affiliation with only one chakra nature)  
Later we discover these can be combined in a number of ways, creating new elements (Mokuton=Doton+Suiton, Ranton=Raiton+Suiton, Youton=Katon+Doton, among several others). From what I understand, these are usually transmitted as a Kekkei Genkai. But I believe they can also be created by the combinations of the elements, by ninja who didn't inherit it from other generations (correct me if I'm wrong). These are not uncommon, but less frequent than the ones above (there are ninja who can master and possess affiliation to more than one chakra nature: Sasuke comes to mind, since he can master both Katon and Raiton. Katon is his clan's natural affiliation, and he mastered Raiton too. However, I don't remember if he has ever combined the both of them)  
Even later, we find about combinations of even more elements by ninja who can master several elements, such as Muu (Nidaime Tsuchikage) and Oonoki (Sandaime Tsuchikage), who can combine Katon, Doton and Fuuton, to create Jinton. These are called Kekkei Touta. I don't know if they can also be transmitted through Kekkei Genkai, or if they can only be taught. They are even rarer than the ones above, since ninja can rarely master or be naturally affiliated to more than two chakra natures (Terumii Mei the Godaime Mizukage, can also master Doton, Katon and Suiton, but I don't think she ever combines more than two at each time). 


My questions are:


Are combinations of chakra natures taught or only transmitted by Kekkei Genkai (or both)?  
Are combinations of more than three chakra natures possible?  
And the above question created a new one for me: Can a ninja master more than three chakra natures? (I think Kakashi does, but I am not quite sure about this)
Chakra element combination is supposedly a born trait. A shinobi is born with one chakra element, and can master a few more (secondary elements).
However, in some clans, such as the Senju, they were born with two elements, (both Earth and Water), and they could naturally combine them to form the Wood element.
Since we only thought that two element combinations were possible, and we discovered that three were indeed possible, I see no reason why there isn't a possibility for four or more.

 EDIT! Based on the latest manga chapters, it seems as if at least 4 element combination is possible. Although it's an initial estimate and the Third might be wrong about it.

We do have some examples for ninja mastering all five chakra elements, Kakuzu is a great example. He had all five chakra elements, Water, Earth, Fire, Lightning and Wind, in one body (though he did cheat and used 5 different hearts for it). So it is possible. It is also said that those who awaken the Rinnegan can master all six elements (Including the YinYang element).
About mixing them together, since that hasn't happened yet, we can't be sure.
EDIT!

 Six Paths Sage Chakra, which creates the Gudodama is called Kekkei-Mora and was confirmed to be a combination of all 6 elements: Fire, water, earth, lightning, wind and YinYang.