Chirpify does not limit the amount of listings you can post. If you are posting listings with images Twitter limits you to about 30 Tweets per day that include images. Best practices will dictate how frequently you should post - you may want to space them out so as not to annoy your followers and stay under Twitter's media limits. Experiment and find the right strategy for your brand and your customers.
The more you post on facebook, the less likely you are to have items catch viral momentum as well.