My 14 year old Yorkshire Terrier recently passed away and I would get another in a heartbeat. Yorkies meet a number of your criteria (although not all).
Pros
They are small - many advantages to a small dog - small poop, don't eat as much, can be carried if necessary, easier to travel with
Medium amount of exercise needed. Yorkies do require walking but not an excessive amount. They can walk far if you want them too despite being small. In her last year, my yorkie went on at least one 10 mile walk.
Hypoallergenic - they require grooming as they have hair rather than fur and do not shed.
They love attention - they are lap dogs and extremely affectionate.
Cons
Training - not as easy to train as other dogs but will be trained. They can just take a bit longer than say a Labrador. I remember house training was difficult but we got there in the end.
Barking - I've put this as a con (even though I never had a problem) as other people constantly asked me if my dog was yappy. She wasn't. I'm not sure if this was a wrong impression generally about the breed or if it's common with the breed. Generally speaking, dogs are yappy when they are bored so it's usually a problem with the owner not giving them enough exercise and/or attention.
Kids - they aren't known for being great with kids, but if you are introducing a puppy into your home, it shouldn't be a problem. Mine never bit but might give a warning nip where it looks like they going to bite but it's more a snap without contact to say you're scaring me! Because they are small I think they learn to be a bit defensive out of necessity.
I got a yorkie because I knew someone else with one and fell in love. They are extremely loving, loyal dogs.
As a general note, I would strongly advise a bitch. Male dogs (even when neutered) tend to be more hyper and territorial. I have experiences of owning and observing both sexes and would never get a male dog in future.