I do not think it makes sense to have followers appear automatically. Have them arise from the story. If the character does not take any inspiring action, why should anybody follow them?
Once they take visible and inspiring action, it's easy to GM-rule that one of the attending NPCs is so smitten they tag along, but maybe it's an Intellect check against the level of the new follower -- does that patriotic speech really work? The character of the follower -- do-gooder, religious fanatic, or complete crackpot -- depends on the recruiting scene as well.
Of course, you can admit the player to "have picked up" a follower between sessions if they insist on the two-week rule from the Focus description, but would advise against that. Have them roleplay for it!
Regarding the specifics of The Strange.
Is the Follower an actual native of the recursion, or does he only exist while the character is present (and has the Leads focus)?
The latter makes little to no sense. Use logic!
is that Follower waiting for her, does she have to seek him out, or does the Follower somehow "know" that she has returned, and seek her?
Whatever makes sense. How deep is the relationship? Does the character have a home base in that recursion? Has the follower thrown away all other ties?
Maybe, one day, the follower gains enough Spark to even tag along across recursions!
ma_il raises an interesting point regarding Spark. The way I understand the setting, everybody who does not have the Spark is on autopilot within their recursion. There is no way such a "character" would attach themselves to a foreign individual that is not part of the "program". Hence, my ruling would be that followers have to have the Spark. If the recursion does not have any such individuals, too bad for the player.