Posters can be 36in x 48in (91.44 cm x 121.92 cm) at maximum. Smaller posters are fine as well. Regarding the orientation, landscape is strongly preferred over portrait as this allows for a larger amount of concurrent viewers.
We recommend the following copy shop close to the venue — roughly 7min walking:
FedEx Office Print & Ship Center
3003 N Charles St, Baltimore, MD 21218, United States