I’ve done similar with my sister’s dog, who now lives with us.
He needs to get used to:
1) Living with you
2) Living at your house
3) Living at your house when you’re not there
in that order.
I’d be really wary of sticking him straight out into the garden for a whole week alone.
Ideally, I’d take two weeks off when you get him, spend the first week with him in and out of the house, then in the second week start to introduce gradually longer periods when you leave him at home on his own.
It will take a good couple of months for him to be properly settled.
Ours is at home alone, with a dogflap out to the back garden, for three days a week (I work from home one day a week, so does the Mrs). He generally does Mon/Tues alone, Wed/Thurs one of us is there, Friday alone and it works okay. On the occasions he goes three days alone you can tell he’s going a bit stir crazy by the end.
Leaving a radio on while you’re out is a good idea, really helps ours.