This may help you:

Your Rescue Dog.
Get as much background as you can glean from the rescue centre or place that you get your dog from. Most rescues will divulge what they have been told but they won’t or can’t give you where the dog has come from if it is a private home. They can tell you if it is a stray off the streets and so has no background. They can tell you if it has come from Ireland or other country. They may be able to tell you a bit about the private home if the private home has given them some background. The rescue should tell you how long the dog has been with them and if they have done any training and socialising with him. They will also tell you if the dog has been neutered. Also, if the dog has had a season. Most rescues microchip. So be careful when stroking the dog down the neck area. Some have a reaction and can get agitated if it is still sore round that area. Ask about inoculations and get a vet certificate stating when the dog was inoculated. Also ask about Kennel Cough as it can be a problem in some kennels.
The age of the dog can be a mystery. Obviously, if a pup then the age can be determined if the teeth have changed to adult ones. This usually happens between 5 and 6 months.
Some of the problems that most likely will occur are the dog not eating when you get him home and not knowing that the place to toilet is outside. So, take the dog to the area that you would like him to use and when the dog is performing introduce a word like hurry-up or be-clean, then praise with either voice or voice and a treat. If the dog does have an accident indoors don’t get cross, just put the dog outside in a safe place and clean it up. Be careful if you decide to introduce new foods. This can either cause an upset tum or a fussy eater. So be careful what you feed if changing over to a different one. When you bring him home be sure that you know where he will sleep. Some dogs are best in the room that you sleep in. It gives them security until they have settled in. Then if you decide to move him to a different place he will be more settled with his surroundings.
Be aware that most rescue dogs have a checkered past. This can be either: aggression in some form and or chasing: either cats, bikes, horses, people, cars and other moving objects. So, keeping on lead for a couple of weeks at least to gauge the dog’s reaction before allowing off lead is a good idea. This will also help with the training of not pulling on lead and also, if using a long line, that all important recall.
Some rescue dog’s can be overly friendly to other people and dogs. So, make sure you warn the person that the dog may jump up and be careful if introducing to another dog. They can take umbrage at an over enthusiastic greeting from an over the top dog. Some rescue dogs will grovel and roll over, be careful when stroking the tummy, some dogs may have been kicked in the past and object to that even though they have rolled over into submission.
If you have had dogs before then sometimes it is a good idea to treat an older dog as though it is a young pup. Start as you did when you first got your new pup all those years ago and not much will go wrong. If you have had rescues before then go with the flow. If in doubt then ask the rescue about the problems that you are
having.
Join an established training group and get as much information from them as to what to look out for. The trainers will have had a lot of experience with rescue dogs and others over the years.

Hi and a warm welcome to the forum. Shelby looks lovely. How long have you had him and did the rescue give you any information on his background (was he a Romanian street dog?).

As others have said, try not to overwhelm him. If he was a street dog, he won't be used to lots of human interaction, probably won't have a clue what toys are but hopefully should interact very well with strange dogs.

A force free (using rewards) training class would be ideal once Shelby has settled in. A good trainer can help you in all areas of caring for your new dog and it is a great way to socialise your dog and also meet new friends yourself.

Personally I would start leaving Shelby immediately - just for very short periods to start with, building up over time. Perhaps give him a stuffed kong or a raw bone to chew on while you are gone. He will need to learn to cope when he is on his own and by slowly building up the time you leave him, he should learn not to worry and realise that you are coming back so there is no panic.