I was able to finish assembling the first unit of handgunners yesterday, and the unit looks nice:
I raided one of the boxes of state troops for extra heads so each handgunner has the same style of hat within the unit. This might cause some problems later when I assemble the swordsmen but it should not be a big issue. On the recommendations of the handgunner expert (Taeklonn), I did not equip the unit with a banner; there is a fifer however.
Other than the head swap with the swordsmen box, these have very little modifications. The leader (equipped with the long rifle) has a plume added to his hat; one gent has his ramrod in the ground in front of him; and two of the handgunners have some extra ammo on their belts.
I was even able to get the handgunners to rank up reasonably well:
Only 7 more units of troops to assemble now!