A serendipitously found dog

This morning my neighbors woke to find a friendly, sweet yellow lab in their backyard--in spite of a closed gate. He had been on the neighborhood email  yesterday in somebody else's yard, and today he ended up in mine--he's an escape artist and kept getting out of the yard next door. I've been thinking about a second dog to keep Scooby company, looking at labradoodles which are mucho expensive, and suddenly with this new dog in my yard I remembered what my mom always said: "The Lord works in mysterous ways." Maybe the Lord meant me to have this dog.
He and Scooby did the usual impolite sniffing routine and got along fine. I tried bringing him in the house but he was shaking he was so scared, and it was clear to me he hadn't had any leash training and had no idea about "Come" or "Stay." Tomorrow, when Jacob's not here, I'll try the house experiment again--letting him in to just the back room with the doors closed. Meantime I've named him Silbey, a contraction of Silly Boy. He is as sweet as can be, but he's also skinny. I carefully fed the two dogs apart but when Silbey turned away from the crumbs in his dish and I let Scooby out, a dogfight ensued. But it's the only trouble we've had. I'd guess Silbey might be a year, not much more. He's obviously worn a collar--there's a mark on his neck--but it's gone. My suspicion is someone deliberately dumped him, because in spite of repeated postings, no one has come forward.
Monday the dog trainer I've used before is coming to assess the situation, and after that I'll take Silbey to the vet--he needs to be neutered, have his shots, etc. I'm a great believer in instinct, and my instinct tells me that this dog can adapt to the house and be a wonderful companion, both for Scooby and me. And for Jacob, who already adores him. But we're a long way from that point, and I know it.
Labradoodles cost$1500 or more but they come crate-trained, neutered, shots up to date, and basic house training. By the time I civilize Silbey I may have spent that much, but I could not bear to let him loose to roam the streets or turn him in to animal control. So for now, I'm playing it day by day. It may be a long weekend. I'll go get a collar and some dog food tomorrow, plus maybe a big dog dish.