Brace yourself, you may get a flaming for even asking the childcare question
but it's a perfectly natural one to ask IMO.
how long to take off? 12 months is normally required by the LA placing the child. The expectation is that you'll need most if not all of that time to start to build the bond with your child. That's not to say you might not use short sessions of childcare, but most of the time it's about the two of you. Intense, draining and terrifying as that is! But necessary, in my one-time experience.
How to choose childcare? Wait and get to know what your child needs, really! Some will prefer a homey atmosphere and a childminder; some will need a nursery to thrive because of other needs. It's massively variable.
Nanny? I wouldn't, personally. Mainly because I want LO to be building their bond with me, not anyone else, and for my LO it would be too confusing. Also many adopted children have a deep need for consistency, and I would feel wary of pinning all my hopes on someone who might leave.
Settling in - slowly, slowly, slowly. Find a nursery (or whatever )that is relaxed about you spending a lot of time there, because gradually and slowly was what worked for us. I suspect it took us four or five times as long to get settled as a birth child might, but it was really worth it.
You will be told that some adopted children won't be able to cope with childcare. This is absolutely true. Depending on their history, and their particular needs, it might be too much change for them. It's impossible to predict whether this will be the case, but you do need to know that it might.
Good luck with your questions - this board is good for those! 