Freedom Isn't Free (Not Even for Dogs)
One of the biggest mistakes that I see pet owners and pet fosters make is putting freedom first and rules second. It's natural to want to "see how it goes" and then - should something go wrong - try to go back and fix it. Maybe the new dog will do just fine eating right next to others? Maybe he won't have potty accidents in the new home? Why crate him if it turns out that he isn't destructive? Maybe he's fine having the run of the place.
Maybe... but maybe not. And sometimes when things go wrong, someone gets hurt. Things get broken. Dogs pick up awful habits or get extensive practice with bad habits that they already had.
When you bring a new dog or puppy into your home for the first time, you've got a unique opportunity because that dog does not yet know quite what to expect in this new environment. He may also be a little nervous and less willing to show his "true" colors for a few more weeks. He's still feeling out the territory and his boundaries with you. THIS is the time to show him what you want. If he already has bad habits, this will likely be the easiest time to break them. If he doesn't have bad habits, this will be an easy time to inadvertently create them.
* Crate train the dog from day one - even if you don't use it later on, it WILL come in handy at some point. Whether it be for grooming, boarding, or traveling, your dog is better off being comfortable in a crate.
* Supervise the dog very closely in his first few weeks. Whether he is two months old or 12 years old, he could have potty accidents or chew on things that he shouldn't. If you're not there to redirect him, you've allowed him to practice behavior that needs to stop.
* Handle introductions slowly and on neutral ground, especially if you have dogs that aren't solid with other dogs or if the new dog's background is unknown. Get a trainer to help, if possible.
* Feed the new dog separate from other animals. Feeding in the crate is ideal as he'll associate the crate with meal time and, if he has food aggression, your other pets and family members will be safe.
If I sound overly cautious, it's because I've seen dogs do some incredibly unexpected things. Sometimes those things are good, but sometimes, not so much. You really never know and it's better to be safe than sorry. Set the dog (and yourself) up for success by giving yourselves time to learn each other and what's expected.