DID= Direct Inward Dial
DOD= Direct Outward Dial
You need to program the DID's under LINES/TRUNKS > DID.
If your provider says you are rotory, then you have to provision the trunks as rotory.
From the information you supplied, you are going to have a conflict- 770-791 are the default numbers for calling groups. You need to know how many digits your provider will be sending. If they are sending 4, and you delete 1 then you will have a conflict with 70 (the main pool). If they are sending 4 and you delete 1 and then insert 4, this gives you an extension range of 4700 thru 4799, inserting 3 gives 3700 thru 3799, etc. If they are sending 3 digits (which are always the last 3 or 700-799) you would delete 1 and insert 4 for an extension range of 400-499 and so on. It boils down to how many digits they are sending and how many you are using and the ranges you are using.