How do I hook this 18-bulb lamp together?
Wow that is a lot of connections for a light. I am surprised the MFG did not send something as that is too many for wire nuts unless you do several sets and connect them together.  I would use a terminal block maybe a little bigger than this but I use this in control panels that are tight on space. I use jumper wires on 1 side then use the other for the connections. They are finger safe but I would put a layer of tape over the screws in this case. 2 tan and red 3M wire nuts connected with a jumper would be safe if that is 14awg wire but that is really pushing the limits.