I kept my young Fell filly on her own for the best part of a year. I was told she would bond more with me if she didn't have another pony for company and I do think there is some truth in this. However, with a bit more experience I now think the most important thing for bonding is to spend one-on-one time with them. They don't have to be alone the rest of the time to bond with you.
It killed me the whole time I had Floss on her own that she clearly would have liked company and couldn't always be with me. Eventually I bought a Fell gelding, both as a more experienced pony to help me learn about keeping and riding a Fell pony on our moorland and as company for Floss, and have kept them together or in sight of each other most of the time since. They don't always get on, and Davy bullies Floss and pinches her food, but they both prefer to be with another pony than not. (The exception being when stabled - Floss much prefers her own bedroom.)
You do get a bit of silliness when you take one away for training, riding, whatever, but it's easily enough overcome with training and practice. (They get used to it, and that the other will return.)
Floss has never wanted to be friends with anything except me and other ponies. She doesn't like sheep, dogs, pigs, cats, chickens, ducks...

Davy is happy to be friendly with anyone and anything, but then he's nothing like as upset if he is kept on his own as Floss is. And I did have a loan Dales pony for a while before getting my own, and she was perfectly happy to be an only pony.
So I would say, it will depend on the pony. Some will be okay without another pony for company, some may enjoy the company of a goat and others may actively dislike the goat. My advice would be, get the boy you want and see how it goes. If he needs another equine, you can put out feelers for roomies such as suggested by MelRice, or companions on loan - lots of people have older ponies they want to continue to be responsible for but would like to be in the day-to-day care of someone else, and to be with another pony that that person doesn't have.
I am excited for you - I embarked on the same adventure 4 years ago and, although I make lots of mistakes and don't do nearly enough with them (mostly time but also lack of knowledge and confidence), I absolutely love having them and couldn't imagine going back to not having my own ponies now. And yes, wish I'd done it years ago.
One thing I would also advise - many Dales will be fine unshod, and they make a lot less mess of your ground if they don't wear shoes. (And if the ground is very wet, shoes can get pulled off in the mud, too.) So I'd make sure you choose one with good hard feet that won't need shoeing.
Happy hunting!