Hi there,
When I was expecting #2, I put #1 in a toddler bed at the age of about 20 months. It went smashingly! Much better than I expected. However, she had been sleeping in a crib alone beforehand.
I would start by putting her in her own bed for naps and see how that goes. If well, try it at bedtime with nice music, nightlight and lovey (or whatever works for her). If that still doesn't work, maybe a mattress on the floor of your bedroom. At least that would free up your bed for your newborn.
As far as getting babies into cribs, there's lots to be said for co-sleeping, so don't let yourself feel too rushed to put baby in a crib by himself. I transitioned both my babies to a crib around 5 months and that worked really well for us.
Good luck and congrats on your soon-to-arrive!