I don't know of anyone that has implemented EasyPost with Store. Store's shipping gateways are undergoing a major overhaul in how they function from v1 to v2 (which is under active development now). Depending on your timeframe I would recommend waiting for v2 to be released (or emailing support@exp-resso.com to see about getting added in to the beta).
There is not an example shipping module per say but you can look at the UPS/USPS/FedEx plugins in the current version of Store to see how things are setup currently as a great starting point. In v2 the shipping plugins are handled as extensions which should make them easier to create and extend.