Hello and welcome to YT

This is a wonderful forum with terrific people, I just joined not too long ago and I have been so impressed by everyones kindness. I'm sure your going to find it just as helpful as I have
I'm so glad that you are taking the time to get information before getting a yorkie too often people dont. Yorkies are a wonderful breed but can be high maintainance with specific needs. Toys breeds are difficult to housetrain and Yorkies are also quite stubborn

It's good to know what you can truly expect.
When I brought Chloe home I continued with the brand of food the breeder was using. When you switch dog foods it can be stressful to their digestive system. If you do decide to switch, the best way is to slowly change over to the new food. Chloe was on Royal Canin which she one day refused. She is now on Nutro small bites and doing well. When she was a puppy I also gave her nutri-cal, a vitamin suppliment each day. Young puppies need a great deal of nutrition and yorkies in particular. One of the possible dangers for a young yorkie is hypoglycemia. This is when blood sugar levels drop. It is a good idea to have some honey on hand should this happen.
If you dont have a vet picked out ask friends with dogs if they have any recommendations. You will want to take your puppy to the vet within 48 hours of picking him/her up. A reputable breeder will allow you to have your little one checked for any health problems and if any are found will take the puppy back. If everything checks out and your little one is healthy the vet will then tell you what vaccinations are needed and when. I suggest purchasing a puppy plan. Most vets offer a package that will include all needles, deworming, exams and spaying or neutering etc. The package is much cheaper than all of these services purchased seperately. Also it is very important to take care of their dental health (yorkies are known for having dental issues). Get your little one used to having their teeth brushed. Even with diligent brushing every second day, my little girl has to go in to have 3 baby teeth removed (she is two) and her teeth cleaned. The cost for this isnt cheap
I did have some questions and concerns after reading your post. You mentioned that you are planning on keeping the puppy crated during the night as well as when you are in school. Would that mean the puppy would be in the crate all night and all day? I'm not sure how long you are in school each day but if you are a fulltime student that could mean being crated as long as 14-16 hours daily. Dogs do not do well on their own as they are social animals and suffer very high stress if left on their own. I am of course only assuming as I dont have all of the information.
Also I hope that you dont take offense by the question as I would never want to make anyone feel insulted. I am only asking as there wasnt much info in your post about how much time you would be able to commit to a new fur-baby or if anyone else in the family has offered to help out. Chloe was originally my DD's dog and I spent alot of time helping with her.
Another thing to consider. Chloe did not tolerate the crate well AT ALL! She hated it and would wail for HOURS. My DD bought the same type of crate as you are planning on getting. We tried with no success to get her to adjust. We followed all of the recommendations and did so for almost a month. I honestly gave up. Putting her through all of that just wasnt worth it. Crate training, like everything else with a puppy takes a huge amount of time and patience. From someone who has kids and dogs believe me when I tell you puppies are ALOT of work. Well worth the work mind you but work none the less. You may find that like me crate training doesnt work out as well as you had planned. Plus these dogs are excellent at manipulating their "mommies"
You had asked how often should you let the puppy loose once you are home. When your home take the puppy out. He or she will need a great deal of play time. If the puppy has been in the crate all day I wouldn't put him back in until bed. S/he going to want and need to play as much as possible.
You mentioned that your grandparents are home all day but that you didnt want the pup out all day. Have you asked if they would be interested in taking him or her out for a "crate break" I have two dogs and the bigger of the two NEVER had the energy of my yorkie. As you have done alot of research you probably know that yorkies are a working breed and as such need a HUGE amount of exersize. Thankfully as they are small much of that can be acommplished at home.
Again I hope that my questions were not off putting. I am hoping that I have been able to offer you some good advice and give you a bit of first hand information on owning a yorkie. I have never loved a dog the way I love Chloe ( thank God my other dog doesnt know LOL) and that is a testiment to how wonderful they are. On the other hand I have had dogs all of my life and I have never had a dog that was as challenging to care for.
Take care and again WELCOME
Tina