General Questions MIMO Communication theory
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.