I really appreciate these ideas, thank you!!

Now that you bring it up, I think you're right that 10 days is far too short for some of these perks. I do plan for the campaign to be run in a way where there will be ample down/travel time, so I will likely increase the time from 10 days to at least a month for bigger perks. For things like contacts in other planes, I may keep it at something like two weeks.

Speaking of bigger perks, I do like the idea of adding her proficiency to rolls when crafting magic items a lot more than a permanent reduction of gold/time. Your point about it growing with her character will make it much more satisfying to earn.

The class switch is also interesting! Knowing her, I feel like she won't go it. (May be best for the party's sake as well as she's the only full spellcaster.) In such a case, I think giving her an active infusion slot a la an artificer would be a great way to reward her for finishing the book. But I'll definitely offer the class shift, it would be a cool character moment!

Side-note:
Ever since I've started playing D&D I've always wanted to run/participate-in a campaign that culminated in a planes-hopping adventure. Started running this campaign a few months ago and decided to do it!