in CEC (canada) the max is 12 on one circuit if connected loads are unknown. If you know exactly what you are plugging in, you may exceed 12 as long as the connected load do not exceed 80% of the rating of breaker. I think 12 is a good rule of thumb.
did you replace bulbs w/ fixture? if so, you can't use a dimmer switch with most compact fluorescent bulbs! you need to either buy dimmable fluorescents or put incandescent back in.
you are not allowed to use a 20A breaker for a lighting circuit in a dwelling unit (residential occupancy). It is against code (CEC). You must use a 15A breaker. It is common practise to not install more than twelve lights on a 15A breaker, regardless of the wattage of bulbs you use.
just leave extra length when chaining the lights together, and use temporary lighting (inexpensive caged incandescents). when you decide to put the drop ceiling in, you can then use whatever lights you want. i wouldn't install fixtures meant for t-bar until the t-bar is installed.