With a white ceiling the reflectors are not needed. The reflectors may cause a dark shadow line above them. Reflectors are great dust collecters and nesting ledges for the occasional bird that finds it's way into the garage.
A good way to check the pipe and fitting threads is to screw the fitting onto the pipe by hand. It should become tight in 3 full turns. Most of the pipe threads I have seen at those big box stores are cut to deep. They bottom out in the fitting before they seal. When using pipe dope it is...