Welcome to Freya, Nance & Sage!
It sounds like you will be like me Freya, not the tummy mummy, so have the time/don't feel sick when looking at a moving computer screen to make lots of posts! I have been totally addicted to this site ever since we found it.
I love your baby's early ultrasound, we had one at 6 weeks ( IVF, they scan, poke & prod you at every opportunity ) and got to see a little heart beat too! It's mind blowing to compare it to a 12 week scan, when the tic tac with a heart beat becomes a baby with arms, legs, fingers & toes as well.
Only two weeks until you get to see Sage again! Why Sage? Is that your chosen name or your nickname while in tummy?

There are some great websites around with lots of practical advice for parenting agreements, donor agreements etc. There is a thread I put up here a while ago which is for a Victorian website but connects to heaps of other sites, including the website for Talking Turkey, which basically gives you a donor agreement form which you can then modify for your needs.
If you put the donors name on the birth certificate, then you will need him to sign off on things like
Passports and if you, as non bio Mum, want to apply for a parenting agreement, the court will insist on notifying him and getting him to either testify that he doesn't want to parent or providing some sort of documentation to say that he doesn't want to be an active parent.
The officials in officialdom at Births, Deaths & Marriages don't like you to say you don't know who the father is, they can apparently make your life very unpleasant if you try and do that, but a lot of couples have asked to have the father on record with B, D & M but leave the space blank on the birth certificate.
Apparently if they have a legalish document which the donor signs, they are happy to do that and it makes it easier with Centrelink/Family payments etc to establish the donor as not being an active father. It's all about establishing intent as well with the donor by having a 'paperwork trail' of agreements etc to show that he is not going to be responsible for the child and shouldn't have to pay child support. ( Apparently they will chase him for that if his name is on the birth certificate and you apply for any sort of benefits from the Government )
There are some great lawyers around who specialise in this sort of thing, so head to some gay & lesbian websites, as some gay friendly law firms advertise specifically for this. They can answer any sort of legal questions you guys have.
Good luck, hope I haven't confused you too much!!