Congratulations on your baby! And on her sleep 
I'd say this is the best time to be getting a good night of sleep, given that your body is recovering and your hormones will still be haywire. My DD is 9 months and is a terrible sleeper, but those first few weeks were particularly bad as I barely had more than an hour of sleep at a time, and almost descended into PND.
I think it sounds like you have a good sleeper there - formula feeding helps a lot with this. Fingers crossed it will continue. Yes, regressions are common. But my friend's baby is 9 months too and with the exception of a couple of nights, she's always done 12 hours solid!
However, if there are bumps in the road - and it is likely because, babies - I'm here to tell you that you can cope! Honestly, you can and you will. I'm also anxious re sleep, and was so worried about how I'd cope. But despite how little sleep I'm getting, most of the time I'm coping. Not all the time, but most! We are more resilient than we realise.
I'm saying this because I know how easily anxiety can spiral out of control, to the point where it will give you insomnia regardless of whether baby is sleeping! And that is a very frustrating place to be, I've been there a lot. Just go with it a day at a time, look after yourself, eat healthily and make the most of the sleep as it's the best thing for your body right now.
can we swap babies please??