Let me answer your questions individually and let me know if you need further clarification.
However, since he is self-employed shouldn't he be able to deduct the mileage for his workdays? The job in each location will be less than 6 months. He leaves his extended-stay hotel each day and drives to different sites where he has to do mapping using a GPS and other such tools.
Yes this would be deductible as laid out in the scenario. Getting from one workplace to another during the course of your business is deductible. This is referenced on page 14 of the link I sent.
He has never worked in the city where he lives. I guess the best thing for him to do is to get a CPA next spring to do his taxes for this year. In the meantime, he is trying to figure out his estimated taxes due this year to make a payment.
A CPA can help but to make the estimated taxes for this year he can use last years tax liability as a proxy if his income and filing status is about the same. So if he paid $5,000 in taxes last year he should make estimated payments of $1,250 every quarter. That would be a good start.
Does his status sound like he would be considered a temporary self-employed person, and as such could he just take the work-related mileage off his taxes?
If he is truly a self-employed person whom files a schedule C for his business then he include the work-related mileage on his taxes as outlined above.
Below is a link that can help with determining the estimated taxes that he should make in 2012. It has good info and includes the voucher forms that he would send in along with his payment.
I think with this link and the info on travel in the first publication I sent he should be in good shape in regards XXXXX XXXXX the info he would need.
Please let me know if you need further clarification.