I know this post is quite old but I'll reply anyway. I live in Alberta and can say that IG's fare well in our climate. They aren't too happy about the colder weather and I do recommend some sort of coat or jammies to make it easier to go outside to potty. ( I wouldn't want to go outside in a t-shirt and shorts when it's that cold, either so I can't blame them )
( How would one behave alone during the day when everyone works fulltime? )
I work full time and my dogs stay in a specially designed room downstairs. I stripped the carpet, sealed and painted the floor for easy cleaning. I put up exercise pens with paper, bedding and water and this is where they stay when I am not at home. I do NOT endorse nor recommend allowing the dogs to roam loose in the house when you're not there to supervise. If they are injured and you aren't due home for hours, that can only spell disaster.
( Can they be trusted off leach supervised? )
NO DOG can be trusted off leash unsupervised. I am going to take this question at face value and say that under no circumstances can you just let the IG outside to potty and leave them to their own devices if you do not have a fenced yard. I do not endorse, nor recommend taking them to off-leash parks and allowing them to run free. There are some exceptions, such as off leash areas that have sections for small dogs. Otherwise, I'd say no. There is no way to control who uses these parks and many people with larger dogs simply don't train them. There are exceptions to this, as well. Please no one get offended and I'm pretty sure we all know the sorts of trouble an IG can get into if they encounter a large, out of control dog who doesn't appreciate little dogs.
( Can I train them to stay OFF furniture? )
Forgive me, but why would you need to train them to stay off the furniture? I can't imagine being cuddle up on the couch watching a movie and not allowing Ari to snuggle with me. IG's are very people oriented and will not comprehend why you don't want to cuddle with them on the furniture. In short, I would say that you probably could train them to do anything but this isn't something that I think is fair to ask of a breed that is so bonded to people.
( I dont want a young puppy - is rescue my best option? )
Rescue is always a wonderful option when looking for an IG.
( How are they generally with potty accidents in the house? )
IG's are notoriously difficult to housetrain but not impossible. There are a lot of housetraining articles on Iggy Planet, with suggestions and methods that have worked well for others in the past, such as using a bell tied to the door and training them to ring it when they want to go out. If you can't handle the odd accident, I wouldn't recommend ANY of the smaller breeds.
( If I'm looking for a low maintenance breed, am I barking up the wrong tree? )
It depends upon your definition of "low maintenance". In comparison with some of the breeds I've come to know over the years, IG's are among the EASIEST to live with. Some may disagree but again, that is because we all define "low maintenance" and "easy to live with" differently. IG's ( as a rule ) are quiet, have no doggy odor, are super easy to train, extremely affectionate, happy, love to play with toys, love to learn. They also get their feelings hurt easily, cannot tolerate harsh punishments or corrections, do not fair well if they are yelled at or hit. They are NOT kennel dogs and do not do well in such environments. They are sensitive to extreme heat and cold, do not like to be left for long periods of time and do love to go everywhere with you, including into the bathroom.
I would recommend reading the sections FAQ, Housetraining 101 and as much of the info provided here for you if you're thinking of adding an IG to your life. There are also many IG breeders here with a wealth of knowledge and experience that they are kind enough to share with us. Continue to ask questions and learn as much as you can BEFORE making the final decision to bring an IG home. Unfortunately, based on your questions alone, I would not recommend an IG for you. I would have to speak to you in more detail to see if I interpreted your questions correctly to see if this is the case. If an IG isn't what you're looking for, I'm sure that I'd be able to assess if another breed might be what you're looking for.
All the best in your search!