Your search can begin during your 3rd and 4th year. The most important decision is to decide WHERE you plan to practice. Your options will be different based on if you desire a saturated, urban area vs a rural area. Once you decide on an area ..... my humble advice is to work as an associate or Corp for the 1st 6-12 months. Learn some speed and how a dental office runs. This gives you TIME to actually research THE AREA where you physically live. It's difficult to find employment or a practice out of state. Not impossible, but difficult. I would rather be in the location physically to do my research.
As others have said .... owning your private practice should be your goal. Start networking. Meet with LOCAL dental equipment sales reps. Local dental practice brokers. Check the local dental society. Visit some dental practices and get opinions from the local dentists. These people can give you more insight to the local dental environment and potential practices for sale.
Again, imho .... I would not consider an ultra expensive practice. I would be looking at a smaller, less expensive practice to buy in which you could build up. I would rather buy an existing small, profitable practice than consider a start-up with no positive cash flow initially.
KEEP your associate or Corp job until your practice grows adequately to dump those temp jobs.
Another option is to find an older dentist who is looking for an Associate leading to partnership.
Plenty of websites with job offerings, but I would prefer the old fashion way of actually going out into the dental community and networking.
As for rules of hiring. I would not sign on for more than 6 months. Depending on urban vs rural .... there will be a non-compete covenent that you will sign.
Good luck.