Talk to your DD about the baby, once you feel comfortable doing so. We told DD1 about DD2 a little while after the 20 week scan, and did the same this time, now were expecting DD3. I ask them what the baby might be doing in my tummy, and tell them how she can hear them, and we talk about what she will be able to do when she is born, etc. Anything encouraging that makes it more real for them. It is always "your baby sister" we talk about too, so it's clear she is "theirs", and not a replacement baby now they are bigger! How much she understands isn't really the issue imo, its more about gradually getting the idea out there that there is a new baby coming, and this is a good thing!!!
Like ohBrother I'd also heard that you shouldn't be holding the baby the first time the older child meets it, and this seemed to work well with DD1 and DD2.
We got a present for the new baby from DD1 (and from DD1 and DD2 this time), and have a present ready for them from the baby. DD1 really enjoyed wrapping the present and decorating the paper, and loved that her baby sister came with a present for her!!! I'll get them both involved in the wrapping this time (need to get on with it actually as having ELCS 2 weeks tomorrow!).
Your DD may want to be involved with "helping" with the baby, and holding it etc. I would say to use this, rather than stop her, if you can. So, you could give her jobs to do (like fetching the wipes or a toy for the baby), or get her to sing songs to entertain the baby while you change the nappies etc, etc. DD1 always wanted to hold DD2, so we'd get her to sit right back on the sofa with her legs out, then lay DD2 over her legs (so she was properly supported), so she could have a cuddle. They bonded really well, and DD1 never felt she was excluded or "banned" from touching the baby. Obv this would all be supervised, and the baby put away safely when you need to leave the room!
A double buggy is the most obvious equipment you'll need. We have a Phil & Ted and it is fantastic - easy to manouvre and no bigger than a single buggy, so no problem getting into shops etc (a side by side buggy or long tandem would be a real problem in the shops where we live). You can go off-road with it too, so it's a nice design to bridge urban / rural use. The baby is well protected in the newborn position (limits the manky finers of strangers being poked into it's face!!!). My two have found the seats really comfortable, never any complaint about not being able to see from the back seat - in fact they are both more likely to want the back seat than the front one for some reason! The back seat isn't particularly low, the way it's angled is pretty good at raising the back child up. We bought our P&T when we had DD1, as we were planning to have at least 2 DC close together. When my friends had their second DC, at least 4 of them bought P&Ts too, partly on the strength of how good ours was.