If you can afford, then you can already come to Cambodia on a 1 month business visa ($25) and extend it later to a 1 year multiple entry visa ($290). Take $25 and a passport-sized photo before landing in Pochentong airport and you can exchange more after exiting customs (usually the last check at airports). Anyone can get the business/ordinary visa, no questions asked and if you can find a room for a short term stay or a cheap hotel/villa on Agoda website, then you can just look for a job and an apartment while staying somewhere.
It's always best to get as much information as possible, whether it's about hotels, jobs or where are apartments advertised. I'm trying to find an apartment with the help of Independent Property Services
But you can also ask Orome
Or post an ad on Expat Advisory
Always research. Make sure you know of all the possible websites where you can look for ads. One thing that bothers me is that Phnom Penh apartments usually only include a maid instead of a washing machine to do the cleaning on your own, otherwise I would already be renting by now. Make sure you find all the job posting websites cause it's not like you're going to find jobs ads for foreigners throughout Phnom Penh. And make sure the hotel is against sex tourism (check their website - being against child exploitation may not guarantee that the hotel will be without prostitutes walking in hallways).
It's also best to visit the country first. I studied about Cambodia for two years from documentaries but I never expected that "sidewalk" means "parking space" here, so you walk on dangerous roads all the time (I always walk on left, facing the traffic) and endless tuk-tuk offers will annoy you. Just ignore them.
The cost depends on your lifestyle. You can rent for $100 in Phsar Thmei or for $1000 in BKK1 area. And while I don't have health insurance yet, it can cost from $300 to $1500. I thought that I'll save money here but it feels more like a place for the rich. Diamond Island is not developing humble properties but large scale Hong Kong style buildings (if you look at project artworks) and I can already see that in the future this place won't be affordable for ordinary cambodians.
And yes, roads are dangerous. I've been here for about a month (2nd visit) and I've witnessed two small accidents caused by idiots who think they can just dive straight into empty space and then they're surprised when they hit someone. I was trying to cross the road and there was less than 2 meters of space but some reckless teenager thought he can still pass before me, so think fast and move faster than the traffic, otherwise they'll try to drive around you right when you step back.... It's madness. And you cross the road by walking through traffic cause no one will stop for you. You'll learn how to navigate through traffic in two weeks.
And while you can buy most items here, it's still best to bring with you as many items as possible. You'll find a Sony MP3 player in Sony stores, for example, but I can't find AKG headphones. But you can find sunscreens, cosmetics with no problem. Check out Sorya or Sovanna shopping centers if you don't know where to shop yet. And the Lucky supermarkets are well stocked and professional. Some aren't that well organized (in one I bought ice-cream that melted before but they managed to re-freeze it).
Are you ready for tropical heat? I am, I brought white sports clothing with me with polyester fabrics that dry up quickly cause cotton t-shirts aren't good enough.