Debs I'm so excited about your news!!! Yours too Bev!!!
I take a month or so off and look what happens - lots more babies!!! lovely.
I decided that there should be as little other disruption as possible in Matthew's life - I wouldn't recommend therefore breaking your ankle late on in pregnancy

- but essentially that meant getting things like potty training and big beds done and out of the way long before the new baby arrived, or not doing it at all until a while after the baby came.
Matthew can climb out of his cot, and has been able to for a long time, but by some miracle chooses only to do this in the morning, not when he goes to bed, so we decided not to take the cot away just yet. Sadie will be sleeping in it eventually, but we'll make the transition in a month or two once he's got over Sadie's arrival. For now she's in a moses basket in our room anyway so we have time. I'm told the last thing you should do is take the cot away and then immediately give it to the baby - that's bad form for siblings
Potty training also for the same reasons - too much upheaval, and in practical terms I didn't want to be having to rush him to the loo to avoid accidents just when the baby decided it needed a feed - so we've left that til Summer as well.
As it is, M waits til I'm feeding S to suddenly decide to do all sorts of things that involve my participation (or my annoyance!)

with something as sensitive as potty training you need to be able to give it your full attention.
In terms of talking about the new baby coming it depends on what your first child can really take in, I didn't start talking about it until I had an obvious bump, and until I was as sure as I could be that all would go well with the pregnancy - ie after 20 weeks - as I didn't want to get him excited (or upset!) about the new baby if it was not to be.
We got a couple of very good children's books about the new baby, at first he didn't really get it, but after a while he started saying there's a baby in mummy's tummy and I primed him on things like what we'd do with the baby - "give it some milk and change its nappy"
Now we're having to read some other books about what babies can and can't do - ie that they're basically pretty boring for toddlers!! as any negative behaviour he has towards her seems to be related to him wanting her to play with him, or he's just a bit too rough with her.
Also we had to talk alot about how babies cry and they're not upset when they cry, usually just hungry or tired. Matthew's childminder had been doing some good stuff talking about it and practising with a doll that cries, which was sweet of her.
Last bit of advice - get some help from friends or relatives to get you time to do the things you normally do with Amy so that she doesn't see a huge difference in her life, but also make sure you get some baby time to yourself as well so if she doesn't already do them, start some routine(ish) experiences like toddler groups, going to a nursery or a minder for a few hours a week so that she can go off and be herself and do her own thing while you get to have a bath, cuddle the baby or in my case, just have it stuck to your boob for entire morning
M was at an age where I felt he needed some alternative care anyway so I found a minder for a couple of mornings a week a few months before S was due, to get him established so he felt it was 'his time' and I wasn't just dumping him with someone else now the baby was here. He loves going to her and it seems to give him some light relief from the baby being in the house most of the time.
Wow! good luck! good to be thinking about it with plenty of time to sort things out
Claire x