GrinGEO,
I haven't anything I can share right now, and am not in front of my GIS workstations so can't even screenshot right now, but some quick points:
There's no need for LAZ - LAS will do fine (LAZ is just an *open* compression mechanism for LAS).
I don't use a combined LAS/LAZ and ortho, or indeed a colourised point cloud. The LAS, and ortho if used, are completely separate ingredients.
Depending on the context, I sometimes do water level work with just a coloured elevation scale like in that video you linked to, other times I will overlay an orthophoto on a DSM to show more detailed impact.
In GlobalMapper I just import either (i) LAS DTM or (ii) LAS DSM + ortho. If using ortho, I then overlay the ortho - so long as both are geo-referenced that's all that's needed, and the DSM and ortho can have different sources.
In GlobalMapper I then activate 3D, click on the [enable water level] button and use the [water level up] / [water level down] buttons to adjust the water level; as you click up/down a box on the screen tells you how high the water is at present. I usually use 0.5m increments; you can set the increment and the starting water height.
Regards
Dave