I have three dogs, just picked up an 11 month old rescue pup two days ago. Our other two are rescues too, and ddog1 was not happy at the appearance of ddog2. She accepted him pretty quickly and now they get along just fine. Ddog3 is currently settling in. Again, ddog1 was not at all happy (she shredded an old tractor tyre in fury) and ddog2 sulked too. They have pretty much accepted her now (still a long road ahead though) which was greatly aided by her being meek around them. Had she tried to throw her weight around and be bossy with them (looking at you, ddog2
), it would have been a much slower and more difficult process.
My dogs are all breeds with very antisocial tendencies (except with immediate family) and they have learnt to get along together. They would all be equally happy on their own with just DH, DS and I too, but again, that's the nature of the breeds, which all three are very typical examples of. Don't underestimate how long it takes, even with dogs which like other dogs, it usually takes a while for the first dog to truly accept the new dog, and requires careful supervision. Don't let that put you off, in my experience its always been well worth it. 
Another thing, our dogs are never left alone, they're always with either DH or myself, usually me, if they were left alone sometimes (and if they were more sociable) I could see it being much nicer for them to have company.
Personally I prefer having more than one dog, and its necessary for us too as we need guard dogs (which are also family pets), and just one isn't really enough.