Solder paste pattern

The core reason for having the center pad separated is that large pads like that may float the ic off the outside pin pads or solder bridge to the pins due to the extra solder paste. Plus, stencil wiping on large pad aperatures tend to fill unevenly. Also, the stencil structural integrity is better with little holes.

There should be around 50-70% coverage of solder paste relative to the pad, there's a good application note here. Full coverage may lead to bridges as solder is pushed outside the pad boundary as there is too much solder on the pad. If in doubt, just pull the edges in a little from the side, rather than trying to make a complex pattern like the one you've downloaded. There may be a reason for it, but it will come from a lot of experimentation.

Thermal vias should be done according to the datasheet. Typically they are top to bottom to access an exposed area for heat to dissipate from, rather than being trapped by the package. It can cause issues by pulling solder through the vias or by raising bumps stopping the package from lying flat.