I have 3 and although Tilly and Caoimhe don't get on particularly well it's a good number for me. I don't know if having more than one dog is 'better' - it depends on the dogs and your situation. Personally for me it is and I wouldn't have just one dog although there are definitely benefits to that - it's easier to go places with one and easier to get one dog looked after etc. Mine do play together but not really all that much, although they are older now at 8, 5 and 3, so they don't tire each other out but they are great company for each other and they definitely do get a lot out of being together - as do I from watching their interactions. Rodaidh and Tilly in particular are very close, he's spent his entire life with her, they do look out for each other and when they do play it's brilliant to watch, they're hilarious
You should be prepared though for them not to necessarily be best mates, as I said before Tilly and Caoimhe don't really like each other, they don't ever fight but Caoimhe, who is very much the boss dog, would bully Tills a bit if she got the chance (which I make sure she doesn't) and Tilly generally mostly stays out of her way so really I'd say they tolerate each other (or Caoimhe tolerates Tills). It doesn't bother me that they're not pally pally, as long as they're all happy then I'm happy to let them sort themselves out as they wish, but I know some people get dogs and expect them to be snuggle buddies and mine definitely aren't.
Other than dog manners, which is important, I wouldn't say mine have really learned much from each other apart from Tilly teaching them to bark at the doorbell and to sit and stare at me when I'm cooking/eating

but I do pretty much all individual walks and training with new pups until they're at a stage where I can take them out on shoots so that's quite a long time - Ro was pushing 18 months before I started walking him regularly with the other dogs and still now at over 3 Caoimhe always walks/trains on her own when I have her here because of her field trialling. I don't really want the dogs teaching pups anything other than manners in their own interactions, the rest of it is my job!
I wouldn't say two dogs is always double the work of one - it is at the beginning if you do individual walks/training etc. (in fact I find it more than double the work at that stage) - but not so much once they're fully grown, you're mostly doing stuff then you'd be doing with one dog anyway. One thing that does increase though is the cost and that is important, it costs me an awful lot to insure 3 dogs (although I also have to pay for extra working insurance for Ro and Caoimhe) and sometimes it feels like there's always one of them at the vet for something or other. Three lots of titre testing/boosters adds up and one £35 pack of Advocate also only lasts me one month!
Overall I would definitely recommend having more than one if you think it suits your existing dog and your situation, but do be aware of the costs, the fact they may not love each other, and also that it definitely does impact your relationship with your existing dog - not always badly by any means, but it does change and sometimes I feel guilty that Tills got pushed out a bit by Rodaidh and then by Caoimhe, and that Ro's nose was put out of joint a bit by Caoimhe coming along. They do adapt though and overall I think they benefit from having each other around

even if they wouldn't always necessarily agree
