Congratulations and welcome to Yorkie Talk.
Safety of taking a pup outside: some people say not until the pup has all of the puppy vaccinations, others say just be careful and limit the area where your pup goes. Other dogs are the main concern, but wild critters also carry disease and can spread it by urinating and eliminating in the yard.
Taking your pup to friends' houses: keep in mind that puppies, especially really little yorkies, need plenty of rest and should not be over-handled, which can lead to hypoglycemia. Have something on hand like Nutrical or white Karo syrup to put a little dab on the gums if necessary. Also, be extra careful with who handles your pup. Many have been dropped and suffered broken legs and more. Last but not least, be wary of what might be on the floor or in your pup's reach at your friends' houses. Not everyone's homes are puppy proofed like yours will be. Potential hidden dangers: electrical cords that can be chewed, a dropped medicine pill or an earring or piece of gum.
Potty training: it is perfectly fine and advisable for you to go outdoors with your pup. Get him accustomed to key words like "go potty." When he goes, praise him profusely, "Good Boy!" Show him how happy you are (without scaring him
). Give him a tiny little treat each time. You are correct that another key to success is to give him ample opportunity to go potty in the right place and that means plenty of trips outdoors.
Crate: if you plan on using one, yes, start immediately. All training is easier the earlier you start. The more a pup experiences early in life, the better off he will be.
Post pictures when you can. Best wishes!