I had a GP appointment at 4 weeks, mainly as 'the books' said it was really important. I got my due date calculated (had already done that) plus advice on folic acid (take it) and standard food advice.
I didn't have a planned midwife appointment until 9 weeks.
Both me and the baby are fine, but I had a lot of problems early on. I felt awful, nauseous, had stomach pain and an early bleed.
I ended up having to call the community midwives myself and got sent to the hospital. The reason I'm telling you this is to say make sure you find out where to go if you do have any problems prior to your midwife appointment. For me even knowing this information was reasurring, and it would have been nicer to have known in advance the relevant phone numbers that to have to seek them out once I had problems.
The other thing you may want to consider, depending on your age, financial situation and personal views is what scans you are entitled to on the NHS and if you want to supplement them.
I wanted an early nuchal fold scan for downs as I'm over 35, and we were getting frustrated as the midwife wouldn't discuss any of this until our 9 week appointment. In the end DP got in touch with a sympathetic GP who found all this out for us. It turns out in our area this isn't available on the NHS. Knowing this at 6 weeks, rather than waiting until the 9 week appointment meant we were able to get booked in to have this done privately at a clinic of our choosing at a time that was convenient to us.
And of course congratulations.
PS As various risks have been mentioned, its always worth reminding yourself that the most statistically likely outcome after getting a positive test result is you'll have a healthy baby in 9 months time