New business help

Hello-
Not sure the proper place to post this-
Im still kinda green to the IT field- (OK VERY green) but I started my own IT gig and actually got a call from a customer.

This is what he needs-
Hes got 12 PCs that he needs unpackaged & setup. Windows is preinstalled.
Some of them will be wired and others wireless (wireless ones will need cards
installed) He currently has a switch setup and all the network wiring IS done.
And then has 2 specific(consecutive) days he needs the job completed and to contact him if I have any questions.

So far Im thinking-
Confirm if this job is a normal business hours vs after hours. Im assuming its normal because of the specific days. But this is information is more for me whether I would need to take time from my current job if its during the day.

Confirm he already has the wireless cards

Confirm whether the network this switch is on is an established network w/other pre-existing nodes or is it from scratch.

Verify the Windows version. Never worked 7 before. Not sure how this would fact into my time to complete.

Is there anything Im missing question-wise?
What would I quote for such an undertaking? This is my biggest job and first one for a non-friend so I certainly dont want to undercharge but at the same rate not overcharge. Right now- I am assuming, this already exists, he just needs someone to just do this for him, the wireless cards have been purchased and its most likely during the day and hes shutting the office down to get this done.
Also- would a flat rate be better than an hourly one? Im kinda gunshy about going hourly and it taking longer than expected. Right now- since Im just getting started the extra time isnt worth muchto me vs getting the job done right and the experience I will take from it.

So any help would be appreciated.
Thanks