I'm glad to hear you are doing well.
My OB's office did u/s for me at 6 and 8 weeks, since I'd had a m/c prior to this pregnancy, which helped me feel better about those early weeks.
I think that how many US you have depends on how many problems you have had in the past. I have not had any complications in the past and I have only had 2 US one at the beginning to find out my due date and one at 20 weeks. But have a ton of US doesn't mean everything is going to be OK. You just have to try to remain positive. If everything feels OK then everything probably is OK, I mean if you not cramping and there is no spotting and you feel OK, then that is a good indication things are OK. I read all the post, and some woman here have an ultra sound every time you turn around, my SIL who is due 5 days after me, has an ultrasound every time she goes to the doctor. But she had a baby with a super low heart rate and she is only 32. A lot depends on your doctor too. If you want more US, you will probably have to change doctors or really pester the doctor you have now and maybe he will let you have more US.
Good luck and let us know what you decide to do and keep us posted on your progress
With DS my odds were 1:170 and with my current pregnancy they were 1:195.
I was pretty happy with my numbers so I saw no need to take on the added risk of CVS.