Yes, you should tie the top course of block together, its called a bond
beam. #4 steel continueous in the top course of your stem/pony
whatever you want to call it... 48inches O.C. solid grout on your
verticle steel and at every corner or door etc....

Regarding height, I build my detached garage 24x36 with 9 foot
ceilings, BUT the car parking spot is set 4 inches lower than the
workspace at grade. So net on the lintel that spans the garage door
opening (8'x16') is 16 inches. Making the net ceiling hieght in the
car park 9'4".