General Questions MIMO Communication theory The following are questions regarding MIMO communication theory. I have come across a MATLAB implementation of MIMO channel. My questions are not regarding the implementation, but rather regarding the theory itself.
In MATLAB there is comm.MIMOChannel that creates a MIMO channel. The following are the properties which one can play with 

 MIMOChannel properties:
%
%   SampleRate                  - Input signal sample rate (Hz)
%   PathDelays                  - Discrete path delay vector (s)
%   AveragePathGains            - Average path gain vector (dB)
%   NormalizePathGains          - Normalize path gains (logical)
%   FadingDistribution          - Rayleigh or Rician fading
%   KFactor                     - Rician K-factor scalar or vector (linear scale)
%   DirectPathDopplerShift      - Doppler shift(s) of line-of-sight component(s) (Hz)
%   DirectPathInitialPhase      - Initial phase(s) of line-of-sight component(s) (rad)
%   MaximumDopplerShift         - Maximum Doppler shift (Hz)
%   DopplerSpectrum             - Doppler spectrum 
%   SpatialCorrelation          - Spatially correlated
%   NumTransmitAntennas         - Number of transmit antennas
%   NumReceiveAntennas          - Number of receive antennas    
%   TransmitCorrelationMatrix   - Transmit correlation matrix (or 3-D array)
%   ReceiveCorrelationMatrix    - Receive correlation matrix (or 3-D array)
%   AntennaSelection            - Optional transmit and/or receive antenna selection
%   NormalizeChannelOutputs     - Normalize channel outputs (logical)
%   RandomStream                - Source of random number stream
%   Seed                        - Initial seed of mt19937ar random number stream
%   PathGainsOutputPort         - Enable path gain output (logical)


I have the following questions: ( I really hope I can get some help)


Does the sample rate mean the actual symbol rate of the input? Is it related to the modulation we use?
Do path delays dictate whether we have a frequency selective or frequency flat fading channel? 
The channel above gives the option of having either Rayleigh or Ricean fading channel gains, I know that Rayleigh is good approximation because of the central limit theorem (i.e large number of random paths), if one specifies that the distribution is Rayleigh, does that mean that the Path Delays should be infinite? Or does this distribution mean a distribution of the path itself.
Why would a Direct PATH (LOS) have a doppler shift different that the maximum doppler shift? Then which one dictates the coherence time? 


Thank you for any advice or answers on any of the above questions
As it says in the documentation, SampleRate is the signal's sampling rate, not the symbol rate.
The path delays together with your symbol rate determine whether the channel is flat or frequency-selective.
You should choose Rayleigh if there is no line-of-sight component in the received signal, and Rice otherwise. Regarding the path delays: the model is that the gain you observe at each sampling instant is the result of many paths, whose arrival times are so close that you can't resolve them. So, in your model, you always have a finite number of paths, each of which has random Gaussian gain.
Each path has a different length and arrival angle, so it can have a different Doppler.


As a side note, and expressing only my opinion, it is more educational to try to create your own models of the fading channel than using a Matlab toolbox. Toolboxes are created to increase an expert's productivity, not for learning.