This hand looks too skinny. What is the simplest way to make it fatter, especially the fingers?
In Edit Mode, you can use the Shrink/Fatten tool. ⎇ AltS
It is limited to the selection.
You can also add a displacement modifier and change the strength value.
For more control assign a vertex group to it. Create a the group and go into weight paint mode ⎈ Ctrl↹ Tab to paint the weights.