Well, first off, dang, that looks good, give me your skill. LOL
Second off, frankly, I’m not as experienced as you so this may be crummy advice, but I’d reccomend either...
1. Building the base shape of the hand by extruding from the wrists then setting up your topology to get the outline of fingers and extruding them
2. Building the base shape of the hand by extruding fron the wrists, then creating some seperate meshes for threnfingers and join them with the main body mesh.
These are just my two thoughts, freel free to experiment. You can also look up tutorials or ask on Blender Artists Community.
(Also, Blender gang, rise up.)