@Ted27 and I were similar adopters - both single, children with some degree of additional needs. I adopted from Kazakhstan 20 years ago and even in the most difficult times I must admit I have never regretted it. Not once. I'm not sure if that makes me resilient or stupid but DS was always worth it.
He had separation anxiety x 1000 when he was little which made returning to work full time impossible and meant my pool of babysitters could be counted on one finger!
He was diagnosed with an executive processing disorder at about 9 and got an EHCP at 10 then diagnosed with a moderate communications disorder (which I'd always suspected) at about 12. There were some very rough times at various point in school to the extent that head of SEN in his new secondary school said to me "I'm not sure he can cope in a mainstream school".
Covid with teenage angst and being cooped up at home with me having a new partner (not living with us I hasten to add) was like the perfect storm of crapness. He got poor GCSE's tried 6th form and hated it, went into a vocational course instead and got the first stage of the qualification after a year then suddenly had an epiphany and talked his way into a sixth form college (still have no idea how!) and went back at 18. Last week he got 2A's at A level and a merit in a Btec and was accepted onto his first choice of university and goes in 4 weeks.
I'm so proud of him I could burst!
Was it most people's idea of a "normal" child rearing experience? Possibly not but it was normal for us and I wouldn't change anything except perhaps wishing he could have had an easier journey for him.
Of course it's easy for me now to look back knowing it all worked out and see it through a rosy halo but in truth I genuinely have never regretted it. I wanted to nurture a small person, I wanted them to see me as mum, I wanted to make a difference in their life, I wanted them to be "mine" - I got all that in spades.
Advice? Agree with the comment about if you're concerned stick with one (or at least until such a time when you can work out how much bandwidth they take up!) and if you can't get real life adoption mates, then the Mumsnet boards can be a lifesaver and other parent of kids with additional needs also really get it and have been great. The "all children do that" brigade can make you feel very lonely.
I'm always reminded of the classic Star Trek saying "it's life Jim, but not as we know it".