Lluna,
First of all congratulations on going through the process & getting your visas. I'll try to be as brief as I possibly can, but i know I can detail a lot of things in our experience.
We were 2007 winners. We did our interview in London, UK & received our visas in early 2007. We did enter the US within 6 months; we didnt want to risk the expiry date on the visas passing us by. That said though, we entered 2 weeks before their expiry, which was cutting it close. On landing at LAX (terminal 2) we were pulled aside soon as we handed over our sealed package (I believe you have something similar in your possession now) - anyway we were taken into a side room and filled out some forms that asked only basic information, we were welcomed into the country & we were on our way after about 30mins.
Because of my job, I had to return to London after a 2 week period. The day I arrived in London is the day our green cards arrived in the post. My wife had my green card securely mailed to me.
During the 2 week period I was in the US, we visited the social security office to sort out our social security. Those also arrived soon after the Green Cards. Also, because she was pregnant & didnt have any medical insurance, we were able to apply & receive Medi-Cal, which covered the cost of giving birth. The application was a day-long process, but we walked away having received our Medi-Cal insurance.
I would return to the US a few weeks before she was due. With passport & Green card in hand, it was an undeniably great feeling bypassing the long Non-US Citizens/Residents queue at LAX and getting through customs and immigration in a flash, especially after always having to wait in the endless Non-UK Citizens queues at Heathrow for an hour or so, then being scrutinized no-end by UK Customs and Immigration. I cant deny how I so totally loved the reverse when entering the US.
My stay was short again & I would leave again soon after our child's birth. My family would leave the US a few months later to join me in the UK when our child was in a position to travel.
In the early part of 2008 I returned to the US by myself to look for work. I had tried applying online and was shown interest, did a few interviews on phone, but companies were more interested in follow-up face-to-face interviews, so I made a trip specifically to find work. I was in the US again for about 2 weeks & spent almost every day interviewing and left when I had a couple of good responses but I didnt get a confirmed job offer till I returned to London.
Soon as I had a confirmed job offer and expected start date, we wrapped up our lives in London and moved permanently to the US. We've been settled here now for 2 years. In all it was a crazy experience moving up and down in bits and pieces over a period of time.
Once when re-entering the US alone, I was pulled aside by customs and immigration and taken to the same room at LAX. Admittedly, I wondered if something was wrong and I asked, but the lady was very pleasant and told me not to worry, that there was nothing wrong - they just had to record my entry again and how long I had been out of the US since my last stay, and that as a new green card permanent resident we were given upto 12 months to completely settle from one country to the US coz they understood that not everyone can just up and leave (Coom, I hope that sheds some light on your question). At least thats what they told me. It only happened once, but I made 2 trips back-and-forth between our initial entry and when we last entered to settle for good.
Concerning housing, we didnt have trouble with that. We initially lived with someone we knew, since we knew that we'd all leave the US after that initial entry. They were kind enough to let us stay with them for a few months - we split bills, etc. But before returning as we wrapped up our stay in London, I used the internet to find an apartment within walking distance from my job, since we didnt have a car. There is plenty of sites that lease apartments. Because we didnt have credit though we had to make a full month's deposit on the rent, unlike say a $400 deposit if you have credit history or at least an existing presence in the US. They management company was considerate of our situation and helped make things as easy as possible for us.