As far as i can tell, keeping opponents within 2 or 3 refresh of your gaming level seems to make sense, esp. for npc mortal casters. Two  -9 pc wizards aren't taking down a -18 npc wizard, but they can probably face a -11 wizard and his -7 underling, or three -6 wizards.

The last combat i ran was 5 -9 refresh characters, 45 levels total, facing a -20 wizard, a -14 monster, and two -5 wizards (-44 refresh)... but the -20 guy could have toasted them if he went full throttle (he had other parts to play). I mean, refinement on specialization and focus items can really put a wizard in a different class.

This was used in game by an NPC to sever an attempted divination by the group, and send a psychic attack back at them.  Also, the group regularly wants to try and interrupt evokers (as doing so is really common in other RPGs).

As the storyteller, choosing the Sponsor's agenda for soulfire is my job (with player input, of course).   What are everyone's thoughts on the possible agenda?

I know for sure that I will be including redemption for any mortal, maintaining the balance between summer and winter, maintaining the strength of the veil between worlds, and resisting outsiders.   Outsiders, demons, and BCVs are all considered "unholy" for my campaign.

we decided for my game that all wal-marts are accorded neutral grounds.

I love it... any reason why?
I've made all UU churches ANG in my games.  Come one, come all...

Mortals can actually be an interesting challenge for a magic heavy group.  It seems counter-intuitive, but attempting to not break the Laws while still neutralizing a threat can be a challenge.  Consider this:  if you physically restrain your opponent, fine.  If you restrain them and then shoot them, Law Breaker!   Shooting at pcs from multiple zones makes it harder to just say "um I use earth magic to bind everyone in my zone."

Plus, while many mortals will wave away their memories of magic, some will become clued-in mortals with a desire for revenge, giving you more fodder for later.

Don't forget presence (for asserting your position), rapport (for using small-talk to break the ice during negotiations, and keep both sides happy), empathy (for reading how happy the client is with your work), investigation (to figure out who did what, so you can then apply the accords to their actions), contacts, and discipline (I'd better pass on the second beer so I can get home and study some more).  

With all that studying, you probably want to just hit the gym instead of rock-climbing or the like, so you might want a little athletics.

I thought the catacombs were partially a result of the plague?

Also, there's a crazy documentary just about Paris sewers, and how they've had to adapt over time.  Not only do you have the catacombs, but you've got miles of old sewer lines, giving you a setting very much like that of underground chicago in Dresden.
http://itotd.com/articles/432/paris-sewers/

There's one article about it, at least. 

I also thought about white court presence and the city of love, but it just seemed too easy... perhaps easy is good though.

Hrm... the champs-elysees used to have a white-light only ban, causing it to be the only place in the world where mcdonald's golden arches were white. I'm not sure if the ban still holds, but it's proximity to elysee castle (and the elysian field mythology, "where heroes go to relax") could mean that the 1 1/4 mile strip of white light could be a calculated occult development... perhaps serving as a sort of "landing strip" or "take-off strip", launching certain beings into the ether.  The veil between worlds (particularly heaven?) could be treated as 2 less in that area, giving angels and the like a more powerful way into the city.  I mean, sure, churches work like that too probably, but come on, why would heaven have NEEDED such a large landing strip?

"My own personal jesus"
Invoke: your own personal jesus, whoever that is, helps you out (bonus to contacts, and resisting feeling alone"
Compel: You yearn to follow people who look like they might be your salvation. Go help them out.

"Cult of personality"
Invoke: resources, contacts, presence, probably more. You're so cool, people just wanna follow you.
Compel: Stupid fans always in the way, and you can't let them get killed.

"Not a girl, not yet a woman"
Invoke: possibly underage sex appeal
Compel: unwanted attention from creeps, plus, trouble getting into clubs

"I hurt myself today, to see if I still feel"
Invoke: any roll to resist physical or mental stress
compel: self-destructive actions

"Fergalicious"
Invoke: resist social stress
Compel: shake your booty randomly

"laid back, with my mind on my money and my money on my mind"
Invoke: keep your cool, except when financial gains or losses are possible
compel: make money, act to keep your money.

"Son of a son of a sailor"
Invoke: anything sailor-y
Compel: drinking & seeking the affections of paid professionals

"'Yo Easy, why's your fly like that?' Easy access!"
Invoke: to quickly produce your... weaponry
compel: inappropriately produce your...weaponry