I'm so glad to see that you are pregnant again. I remember your story! I wish for you that everything goes well this time.
I can understand your anxiety surrounding the possiblity of multiples. Only a few months ago my partner and I felt the same way. My beta #s were not quite as high as yours (around 400 at 14 or 15 dpo and just about 900 48 hours later) and I'm now almost 18 weeks pregnant with fraternal twins.
We are adjusting, excited, scared, nervous and happy. It's an incredible journey.