seems you have quite a job on your hands here so lets go back to basics to cover you first question all you can really do is dig the trench.
1) first thou you need to identify the connection hereon called the optus connection and find out if it is two core telstra line, coaxil cable or optical.
Seems quite unusual you cant get it dug because people who do trenches for a job usually wouldn't be bothered by a few services because they know what they are doing and can work around them but if you want to do it yourself go for it.
you will need to dig a trench not less than 600mm deep from next to the service pole (stobie pole) to your house and not less than 300 mm wide.
in this you will need to place two conduits one 32mm heavy duty orange for single phase connection 40mm for three phase and one comms conduit that is actualy water pressure pipe go 25 or 32mm to be sure ensure they are seperated by at least 100mm the whole way and do not cross over each other in any places.
You will need to get some large sweep bends for both the power and comms.
At the house side bring the conduits up out the ground prferably under existing the service fuse position on the side of the house and leave it there, same for the phone.
The cheapest way to connect the power will be to get the electrician to install a metal water pipe galv 50mm for mechanical protection up the side of the wall with the electrical conduit inside up to the position of the existing service fuse holder witch will become redundant.
For the optus whitch i suspect is telstra you will need to inlist the help of the service provider or a licenced data cabler who will be able to extend and redirect this to the house.
from the house run under the ground in the trench you have dug as directly as possible and using the previously mentioned sweep bends avaliable from http://electriciansupplies.com.au/ or a electrical wholesaler to the bottom of the sevice pole and stop. put some rope through the conduits tie them off and tape it all up to prevent water entering.
Back fill the trench half way (i suggest using dolomite sand for this bit as a identifier but not technically required as was pointed out in previous topics) then place the marker tape for the electrical and comms also avaliable from sparky supplies or a friendly sparkie and then back fill the rest.
if you arent enlisting a electrican friend i would suggest taking lots of photos as proof of job done properly and thats about all a diy-er can legaly do.
2) You cannot install the cable youself so just forget it.
3) no they cannot share the same conduit unless you have fibre optic and thats even not advisable.
4) you can install a pole but your not saving much in this case and there pretty ugly.
hope some of this helps.