Moving and an SN kid (kinda long)

I might be getting way ahead of myself but I'm a 'planner'.  Anyway, things are looking good on DH and maybe putting in an offer on a condominium in the very near future (viewing #2 happens this weekend) and it just hit me last night as I was looking around our current tiny apt and thinking "yes I'm happy that maybe we're moving but also sad, both my boys came home from the hospital to this apt, so many memories" as I look at the door frame where Chris's height marks are - 12 mos, 18 mos, etc and then it hit me - OMG HOW IS CHRIS GOING TO DEAL WITH THIS?

Right now we share a two family home with my parents - this is the only home he has ever known.  How is he going to react when "home" isn't the home he's used to?  He does pretty well when we go to my in-laws - he knows where our room is and that's his retreat but I can't help but now be worried about how this transition will be for him.

If any of you have experience with moving and how to help you LO with the transition, I'd welcome some advice.  We'd be moving from close quarters - it's a one bedroom with an 'annex' off the master bedroom - it used to be our home office but now it's Chris's room - there's a divider in between his room and ours but it's open most of the time and we converted our large walk-in closet into a nursery for the baby so that's another one who's used to being very close to mom and dad.  

We know we need bigger space but I'm terrified of not being able to take a quick peek at the boys at any point during the night - and wondering what safety precautions we'll need to take as Chris can sometimes be a wanderer.  One day, while I was out, DH was changing the baby and the next thing he knew, Chris had gone downstairs, opened the front door and was OUTSIDE IN THE MIDDLE OF THE STREET.  Nothing happened other than everyone got the scare of their lives.  So of course I'm now thinking of the apt in terms of 'can he get out?  how?  what precautions can we take?'

Sorry for the ramble but you know how it is - everything gets just that more complicated when we have to factor in EVERY family members' needs.  

 :-)