Just to confirm that if there is any mention of Holland/Shmolland then I for one will bring DD1 down to mumsnet towers to eat your desk. I rather like Holland, as it goes. SN is absolutely nothing like it.
Thoughts of the top of my head .... eek ...
Be prepared for friends and relations to let you down when you need them most.
Grandparents are as upset by the possibility there is a problem as you are. But they have the luxury of being far enough away that - particularly with conditions like ASD - they can pretend there's no problem. Would they rather think you were a bad parent or their beloved grandchild was disabled? It's just human nature to go with the most painless option, but it means you'll be undermined by your own mother when you least expect it.
Friends have two problems:
Firstly, the natural tendancy amongst parents to be reassuring: "oh, it's OK, little Jack does that all the time". It's comforting if you are talking about licking the window to see how it tastes. It's not comforting if you are talking about standing licking the window for hours and hours - in fact you will feel belittled and possibly want to kill them, but until you have an SN child yourself you don't realise the difference.
Secondly, there's still a huge taboo/embarassment around Special Needs. You won't see it any more, because your child is still just a child who now (hopefully) happens to have a diagnosis. But to them, however tactful they are, a tragedy has happened and your baby has turned into a freak. Good friends will get over this and quickly move into the same space as you. Bad ones won't. But again, the initial reaction is just human nature and generally leads to a period where no-one speaks to you for fear of saying the wrong thing. Keep talking to the good friends and educate them gently.
Other key things: there is a huge amount of advice and moral support (if not practical support) out there. It's mostly unofficial like this forum and no-one in the official agencies will point you this way. But this is where you learn about DLA, Portage, SALT, statementing, AFOs, DAFOs etc. etc. Jump into a relevant forum as soon as you can bear to.
What else: oh do not be fobbed off by the ignorant (usually social workers and health visitors, training seems a bit patchy in those professions) wittering on about the perils of "labelling" your child, as if this was somehow going to wreck their life. I don't know what poisonous little political weasel thought that one up to save money, but it's bollox. It's not a "label" it's a "diagnosis" and a diagnosis is the gateway to therapy and services which can change your child's life.