The best way for the wizard to defend a spellbook is the same as the best way for you to protect your precious computer files - have multiple backups.
But, if he hasn't had time to make a copy, if he knows someone is trying to steal the book back, he wouldn't leave the book in the shop overnight. He'd keep it on himself, likely guarded by as many guards as a 7th level wizard can afford to hire on a temporary basis.
If he must leave the book in the shop for plot points, he'd certainly have the book very well protected and secured. He's 7th level, so he knows 4th level spells. He might, for example, use Stone Shape to fabricate a 'doorless' safe in a wall or floor block. And he'd certainly know to keep the book in a lead box to block scrying and detection attempts. He could also use illusions to hide/conceal the book. And decoy books and safes to waste the thieves' time. And of course, a 1st level Alarm spell on the shop would work wonders. He might hire a dozen men at arms who hang out in a neighboring building waiting for the alarm to go off.
You say he can't use anything too damaging in terms of traps. Well, poison gas doesn't cause much physical damage and dissipates after a while. And while you say its illegal for him to create fatal traps, a) he may not care, b) bribes and Charm Person can get the well-to-do out of trouble, and c) dead thieves can't report you to the town guard. If you don't want to do that, you can always fill the shop with a Web.
Beyond defending his shop, since he knows there's likely going to be a break-in, he might have a familiar watch the shop from a distance and follow the thieves back to their home/inn/hideout. And when they aren't looking, he can rob them blind.
Yes & No
Generally Freewalker seems weaker than the PHB classes, but the 15th level powers are simply broken.
- It has spell progression similar to a Paladin or Ranger, implying it should be compared to those classes.
- It has no listed class features besides Spellcasting and the four School abilities. No Attribute Increases, no class defining abilities, nothing. It also has an AC of 10 + DEX, unlike the Monk or Barbarian. That's absurdly weak.
- What abilities the class does have are inconsistent with PHB class abilities (i.e. per day instead of per rest, static bonuses instead of Advantage, etc.), though most are of a similar power to PHB abilities.
- The overpowered abilities are Master Caster and Death Blow.
- Master Caster is crazy powerful, and will only become stronger as new Abjuration, Divination, and Transmutation spells are published. With the restrictions in place, this one looks fairly reasonable, but play testing will show that it is actually very strong.
- Death Blow is better than a Vorpal weapon or a Slaying weapon. Death Blow guarantees that one combatant is out of the fight. It's campaign destroyingly powerful - imagine your players' response if an NPC used that ability on them. Or consider what it means for the big bad if a player uses this ability - hit for 3 damage, and the final boss fight is over.
- If Death Blow were to be modeled on Vorpal, Arrow of Slaying, or similar abilities then it would be a cool signature ability. As presented, it is a campaign destroying joke.
Good luck. I hope this feedback helps you design a more satisfactory iteration.
Best Answer
While I whole-heartedly support your quest for a fine moustache, I'm afraid the best you can reasonably manage with prestidigitation is a moustache tattoo. The relevant bits of the spell are:
As written, it appears that you'll need to re-cast prestidigitation every round to maintain a physical moustache, but if you go for a moustache tattoo, the mark will be maintained for up to an hour with no additional effort on your part.