You should look in a linear book (or online) to see how one typically finds eigenvectors. And while you're at it, look up "diagonalization".
The point of diagonalization here is this: if D is diagonal, say with entries d_1, ..., d_n down the diagonal, then e^D will be diagonal entries...
There's no reason to be ashamed. I only wanted to know what flavor of the subject you enjoy before suggesting people/schools.
Perhaps you can read up on the different types of representation theory and then let me know which ones strike your fancy. If you're not sure where to begin, I can make...
Each R will be what you get if you do the row operation to the identity matrix. E.g. if you do the row operation that swaps rows 1 and 3, then R will be the identity matrix with rows 1 and 3 swapped.
What if 0 is an eigenvalue?
No. Consider ##\left( \begin{smallmatrix} 1 & 1 \\ 0 & 1 \end{smallmatrix} \right)##.
If A^2=-I then det(A^2)=det(-I). Try to see if you can use this to answer your question.
I think what's confusing you is the difference between an "internal direct sum" (in which you write a vector space as a direct sum of subspaces) and an "external direct sum" (in which you take two vector spaces and add them together, without reference to them being contained in a larger vector...
The rref of A is of the form GA for some invertible matrix G, so the solution sets to Ax=b and rref(A)x=b will generally be different. The precise fact to note is: if Ax=b then rref(A)x=(GA)x=G(Ax)=Gb. Note that if b=0 then the previous computation yields rref(A)x=0; and conversely, if...
A rational function is the ratio of two polynomials. You observed if there's anything "funky" in the denominator, then certainly R won't get mapped to (0,1). Now just think about what "funky" really means.. Remember, the denominator is a polynomial.
Edit: Sorry--that's not really helpful...