the best season to go xin jiang is mid sept to end oct....if you only have March or June, than the best will be mid may to early june...after that ..will be hot....March will still be quite cold ...
U dun really need a guide lah..its very easy to travel in xinjiang...they have bus, plane,or train to most of the major city....
I fly in to Lanzhou and travel westward passing jia yu guan, dun huang...and took a over nite train to urumqi....than from urumqi got a local 4day tour package to Kanas...and than went back to urumqi...after that took a plane to kashgar....and than book a 4wd for 2days to go tashkurgan (book the 4wd from John's cafe) ...and after that book another 5days 4WD(from John) to cut across the taklamakan desert to reach turpan...total took me almost 20days for this trip....thru out the whole trip I did not even book a single hotel...just find 1 when I reach the city...my backup plan is sleep at the train stations or some hotel lobby the most...hahaa