One of your questions is easy, in this line
exten => 7051,n,Dial(PJSIP/555-555-5555@myVOIPprovider,,D(wwwwww705))
The variable ${EXTEN} is equal to the extension or ‘7051’, so you can use this or variations of it for substituting the dialed digits.
The CallerID issue I am not sure about, but you might have success using a dial string like this:
Dial(local/555-555-5555@outbound-allroutes)