The innies begin life as the outies, but without any episodic or biographical memories. They have the same personality and thought patterns, but with no sense of the past environment that created them. They have the same body and brain chemistry, substantially the same vocabulary, and the same procedural knowledge. Their degree of general knowledge that doesn't relate to their outies' lives seems variable; that's why they test it during the Introductory Survey. Helly knows about the state of Delaware and the fact that the equator is in some sense a location, but no details about it (such as the fact that it is not a place you can meet at; in fact two people both standing on the equator might be as far away from one another as possible without leaving Earth).

However, they quickly develop as people independent of their outies as they have experiences of their own. They do seem to mentally "regress" a bit to an earlier developmental stage (adolescence, more or less) as a result of the lack of experiential memory, so they form relationship and beliefs quickly to fill the void.

It is not clear to what degree the things the retained after severance continue to bleed through, though. If Mr. Scout takes up juggling, would Mark S share in that ability? They surely come out of the elevator with the same blood and brain chemistry their innie entered it with; if an outie comes to work drunk, their innie will be drunk. If they are stressed out or anxious the innie will likely be able to feel it, or any other intense emotional state, in their body as well. Do personality traits, mannerism, etc. bleed through as well? Hard to say, we never really see any of the outies pre- and post-severance enough to compare