Similar to this question on Red box to 4e core rules upgrade, what problems are there overcome with or good ways to achieve moving games and characters from the Beginner Box rules to Pathfinder Core Rules?
I'm planning to work with the players to pull individual rules/spells/skills etc. in to the game as they would like and am happy to adjudicate any issues that arise from that, but am curious about any game breaking changes.
I know the Beginner Box rules are compatible with the full rules, but are there any problems cause by starting with only a subset of the rules? Can PCs with core character sheets be played alongside PCs with Beginner Box character sheets without problems? Are there any problems with applying new rules piecemeal? Etc.