Lots of people use a friend or family member’s U.S. address until their plans are more settled. It would help if it were someone with whom you have a good enough relationship that you can trust them to notify you about/forward correspondence. You will have the opportunity to change the address later, say if you get a job offer somewhere and sign a lease, etc. Plans do change, and the process does allow for that. You will need to show that you have the intent to establish a domicile in the U.S., but not necessarily that you have actually done so by the time of the interview.
Normally at the immigrant visa interview, the interviewing officer will review the application line by line and ask if there are any changes. (For example, it’s not terribly unusual for people in the process to be younger people who married much more recently, and entirely possible for children to be added in the meantime.)
Here’s what the State Department has to say about establishing a U.S. domicile:
"When a sponsor has clearly not maintained a domicile in the United States, he/she must re-establish a U.S. domicile to be a sponsor. The aspiring sponsor may take steps, including the examples given below, to show that the United States is his/her principal place of residence.
Find employment in the United States
Secure a residence in the United States
Register children in U.S. schools
Relinquish residence abroad
Other evidence of a U.S. residence
If the sponsor establishes U.S. domicile, it is not necessary for the sponsor to go to the United States before the sponsored family members. However, the sponsor must return to the United States to live before the sponsored immigrant may enter the United States. The sponsored immigrant must enter the United States with or after the sponsor."
So putting your condo on the market is one step to establish domicile in the U.S. My office usually tells people to make sure they have set up U.S. bank accounts, credit cards, voter registration if possible, library cards, etc. If you’ve applied for jobs in the States yet, keep the details about those applications, too.
Good luck, and glad the I-130 stage was fast and uneventful! Not that I expected anything else, though.