ladyhobbit, your Roku will work with Comcast. It's only HBOGO with Comcast that wont.
My Roku 2XS is 27 feet and a door and wall away from my wireless router and works fine. Signal strength is Excellent the majority of the time. The only way you may have problems is if there's a lot of wireless traffic in the apartment building. If so, just try different wireless channel settings in the wireless router.