Time-spread multiple echoing of audio signals
I'm not that familiar with the technique but reading up it looks like you basically just want an echoic convolution kernel of some sort which you can apply. I don't think the kernel you are building there is correct - if you want, for example, a single echo then the convolution kernel would need to contain two impulses, one at zero offset and one offset into the kernel by the time delay of the echo. For further echoes you would want further impulses, again offset into the kernel by their delay amount. You can have more sophisticated echo kernels but I would suggest this as a starting point



In response to question 2 I would not crop your signal unless it is particularly important to keep the length the same. Keeping the tail will make the deconvolution more accurate and unless your kernal is huge it won't be a very noticeable extension of the signal.