Having run a solo campaign for a dear friend of mine, I can offer a few crunchy bits from a DM perspective, if they might help:
1) You'll want to design encounters with the following key points in mind:
a) CR will be = to APL -3. My player was a druid with a hippo companion, and at 1st level I had her facing mites and kobolds, as well as low-level vermin, and single monster encounters. She did well and that kept the challenge at a reasonable level. (CR 1/4 at 1st, for example)
b) as stated in Gamemastery Guide, be extremely careful with traps. Obstacle traps like a portucullis trap probably wouldn't slow a barbarian down much, but magical traps are going to be brutal.
c) seed treasure with plenty of disposable goods, especially potions. Giving a solo PC extra treasure in the form of disposable goods doesn't break the game, and helps off-set other class abilities that are missing as well.
d) monster selection is best done by comparing character ability vs. special attacks and defenses, as well as movement modes. A spell resistance and attacks vs. Fortitude won't matter much to a Barbarian, but you put her up against a spellcaster who knows fly and Will-based spells, and it's game over. Pay special attention to her combat style and play to that. Pay close attention to her feat selections, and use that to guide enemy selection.
e) although this may sound like cheating, always give her the option of some sort of escape plan. When you have a mastermind villian you'd like reappear in another adventure, you give them an escape route since they are unique, and in a solo game, it's the PC that is unique, and should have an option of escape for self-preservation.
2) I can't help much with Kellids as it sounds like you have a wealth of info anyway, but you might look at Humans of Golarion if you haven't yet.
3) Just as an idea, the ferret could begin with an altered bag of holding-type pouch that the characters awaken with as a "blessing" that doubles as its home to prevent it from being sold. A bag of holding is a useful, but not overly powerful item that won't break the game, and solves a few problems for you.
Here's just a few ideas and lessons I've learned to get the ball rolling :). BEST OF LUCK!! Hope you have a blast with it! :D
The Pale :)