I have personally never seen anyone on this forum move in with someone (even friends) and start a poly relationship with them at the same time and come back to tell us of their success. Generally, they come back asking for advice and support with what's happened since the move (very bad, unexpected things), or hint at trouble then drop off the face of the planet.
If you must do this, please do your research on foundations, and actually, there's a really good list of questions from another group I'm part of that's a very good start to figuring out what everyone wants. You should sit down, the three of you, and make sure you're in agreement about these things.
i.e. can i/we give possibility of long term commitment? living together? life/future? marriage? (or are we a closed group?) can i/we offer fluid bonding at any point? can we define what safe sex means to us? can i/we offer shared events, outings, vacations, etc. (or do we need connections who are willing to be background or portrayed as friends, not romantic partners?) can i/we offer a level of connection where communication and/or seeing each other daily is feasible?
can i/we give partners support of any other connection? (or is there a want or expectation for approval and/or vetos?) can i/we give support of newer relationships even if the primary connection develops problems? (or is there an expectation that other love would be reduced or disposed of?) can i/we offer support from the start and along the way? (or is there a probation period?) can i/we offer support of a new love making plans for time and projects with our partner(s)? (or are time and project decisions made from within the existing relationship?) can we support informing each other of plans? (or do we intend to grant or deny permission?) can i/we offer support of individual connections? (or is overlap and/or love/sex all directions required?) can i/we offer support even if some of the connections shift?
can i/we offer privacy of intimate moments? (or is there an expectation that everything must be share-able?) can i/we offer financial intertwinement? having kids? parenting? can i/we offer an actual *place* for other loves to visit/sleep? does that involve existing partners giving up beds and/or bedrooms? can i/we be ok with that? (or do other loves need to come with their own place, car, and/or finances for hotel rooms?) etc.