Only one episode really dealt with the Romulan homeworld in depth. If the Remans were the slave race that was building the Romulan ships, they would have already had sufficient education to build a powerful warship. During the war, they would have had the resources to scout out a location, as well as sources of supplies to build the Scimitar.. As for Picard not being important enough to replace, he was one of the Federation's most prestigious and someone likely to ascend to a key position in the Starfleet hierarchy in the near future. He became captain of the Federation's flagship, and was offered a promotion to the admiralty in season 1. Regarding critical information, the Romulans were shown to have the technology to rip information from someone's mind.