Need Advise for dog!!

I have a dog he is probably mix breed don't know which one day he just came to our house when he was puppy and we adopted him now he is around 3 years old we haven't vaccinated him and genuinely i don't know anything about vaccination when we hot him now i started to know. My dog generally roms free on street and play with other dog in neighborhood and we take him when he wants to come home its his msty daily life, as we are vegetarian we don't give him meet or non veg much, sometimes eggs or pedigree or chew bones, his diet is more like veg mostly and some egg cake,

Questions. So should i vaccinat him now is good to vaccinate him at this age for firat time or its going to be fine also one time municipal dog guys get him for population control surgery he returned after 3 days, so he had population control surgery. He sleep with us on bed. I need genuine advice what should i do to protect him or my family, also if there is oral medicine which is best as i have no convenience to take him to vet he doesn't sit on bike.

Really appreciate your advice