1, Yes only connect one end. I would connect it to the end with the best grounding system. This usually means at the plc or DCS system, not the transmitter.
2, As long as the DC common is connected back to ground somwhere I think it would be ok.
3, The AC ground Should be connected back to ground too, but you need to make sure you have a good ground. If you dont you could get alot of noise if the AC line shorts to ground.
P.S in another post you said you were working on a modbus project, you should go to ebay and search for vHMIAutomation "But dont get the HMI source code, its very complex" take a year to figure out plus there's no comments
but checkout his Modbus Driver . This Driver was reading 62 DM at a wack 3 times a second , this is the link. I have an example on how to use it if you buy the Dll from him.
No development or runtime license keys
No software copy protection
No activation or registration serial numbers
Best of all , you can get it for $19.99
http://cgi.msn.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11806&item=3807887641&rd=1&ssPageName=WDVW
