I'm sorry I also have no experience with Simulink for Power Electronics so I can not help you with any issues that are specific to that package.
The repeating sequence block is part of the basic Simulink package so I am familiar with that.
Sorry, I didn't read your question carefully enough. I see now that you wanted to make a triangle wave, rather than a sawtooth. Yes if you just define two points, as I originally described, it will make a sawtooth.
To make a triangle wave please use:
Time Values [0 T/2 T]
Output Values [0 A 0]
I think that the sample frequency of the simulation is determined by the solver, and may be either fixed step size or variable depending upon what you select. Generally Simulink is good at choosing a high enough frequency to give a stable and accurate simulation. In any case the appropriate sampling rate (step size) for the simulation depends upon the dynamics of the components in the system and generally will not depend upon the repetition period of your source waveform (Although the step size certainly has to be smaller than T and perhaps T may be a multiple of the step size)
