I used to be a nanny and often looked after the kids while the parents went away, that was with kids i had been looking after for a while. I would go for it if i was you and between now and then approach a nanny agency and tell them what you want and try a few of the nannies out to make sure you are comfortable before you go.

if you are planning on leaving your car for the nanny to use it might be a good idea to go for a drive in it with the nanny driving, i did that for a family that had a brand new expensive 4wd. if possible get them to live in with you for a week and do all the normal things you would do with the kids so they can see your routine, get them to make the kids dinner, do the kids washing etc