I'm not too sure, since I've never checked with no points in my account. However, due to a web site glitch, it sometimes forgets who I am and what I have in points (the message is Not Enough Points), but it still allows me to check out award availability.

Officially, there are no capacity controls or room type limitations - however, many of us have noticed that some rooms (suites, etc) are available for purchase but do not show up as available for awards. This varies by property.

The long and short of it is that Choice is not as vigilant as we might wish in enforcing their own rules.