Lying east of the Dasht-e Lut desert, Zahedan is the main economic center of the region and home to many small- and medium-scale industries. Its main products include cotton textiles, woven and hand-knotted rugs. but unfortunately there are not much opportunites to visit as a tourist in the city. however you can still visit university to see local youth or bazars for some shopping, but remember zahedan is more expensive than other places. and due pakistans influence zahedanians are bit unfair and cheaters.
you can find busses for border from main bus stop of Quetta. but the condition is just average according to the busses runing in the rest of the country, but still it is far more better way to travel by bus then the train. this pic of bus is near the wall of iranian immigration office, but in pakistani side.
if coming from pakistan, i would suggest you to reach Pak-Iran border as early as possible, but most of the buses running from Quetta to Taftan reaches at about afternoon (12 a.m) however leaving Quetta early evening but they pick lots of stuff from in-between and also they travel quite slow, and condition of road upto 250 km in start from Quetta is not good. but if you are reaching at about 8 a.m to 10 a.m you can catch bus from border to Zahidan which cost 1500 toman per person or if you are entering late than you can only get taxis which will take around 6000-10000 per head, and tavelling in the city like all other cites is on city busses or the cars also run as "sabaris" take mixtures of travelers from spot to spot.
there is an other option which i used once and still cursing on myself is going by train from Quetta to Zahidan. there is a train service twice a month but it takes almost 30 hours to reach the border and it stops so much so my strong suggestion is to take a bus or you can fly from Quetta to Mashahd (every sunday) by PIA, also cheap and easy option.
as i have said earlier, zahedan due to being so close to pakistan, has got lots of influence from neighboring country, however temperature is hot but attitude is same like any city of pakistan. locals are shrewd, unfriendly and hawkish, must be careful of your pockets also when in bazars. lots of pakistanis work here.
my suggestion is quit the city from your itinerary and go directly to kerman which is 7 hours distance by bus.
An other main problem which can happen would be the money changing. one must be watchful while changing, the best conversion rate of Pak ruppee will be available at the pakistani side of border.