Hi OP, hope you and your beautiful baby are doing ok.
I've worked with adults with learning disabilities and my DP is an autism specialist. We have a 1 year old and over the last year we've often mentioned how her latest thing really reminds us of someone we've worked with. We have no reason to think she has autism, it's just her regular baby development that would be a sign in someone older. The scratching she did lots, then it was hitting with an open palm, it was her learning how to grab things. She also used to love particular patterns or textures. She was very attached to a pair of pyjamas I had and would look at the material, and do the reaching/scratching for a quarter of an hour uninterrupted. She used to flap her hands about when she was happy or excited, now she might clap or wave instead but still does it a bit. All babies do something like this when they're learning to use their hands.
She didn't stop making sounds for as long as you and pps have mentioned, but I remember a time when she would only 'chat' some days and only first thing in the morning. After that I'd lost my chance. Who knows! In terms of forgetting how to do things, though, she was completely determined to roll over and would try to roll whenever she was lying down (this must have been post 3 months as before then she hated being put down) she then rolled over twice, and forgot about it completely. I had to teach her again just before she turned 1 because she would be cruising along, fall on her back, and be completely immobilised. She still doesn't roll over while asleep.
Because of our backgrounds we're probably quite relaxed about autism as we know we couldn't really spot it this early, but I have been incredibly anxious about plenty of things, and still google stuff all the time. I wish babies came with an 'all ok' indicator so I could limit my worrying to when it started flashing red!
If you do end up getting an autism diagnosis then I'd just like to say that sometimes the picture we get from the media (and dr google) of autism is way off the reality. DP and I have several friends and colleagues between us who are autistic and they are as different to each other as you and I are. A couple of them feel autism is an important facet of their personality, and others are more private so few people probably know about it.
As you have the referral now, you're doing all you can do, so I hope you can enjoy some time with your baby.