I'd say dog here, but I'm biased due to being allergic to cats. XD
far as concerns for dogs go, guess I could try giving some limited experience. I'll put it in a spoiler since it might get kind of lengthy.
1.) Really depends on the breed, dogs such as pugs can be kind of costly due to some skin conditions, their bulgy eyes, and shorter snouts which lead to breathing problems, acne can also come up.
Not entirely sure on grooming, some dogs have 2 coats so shedding can be an issue (pugs again) and can be stubborn about getting their nails clipped. From what I've seen bathing isn't too much of an issue, maybe once every few months wouldn't hurt. Not sure how much professional grooming would cost since we mostly do it ourselves.
Food wise, think it's ~15 to 20 bucks for the bigger bags of food that last a while and maybe 3 to 5 for treats. I can't say for sure on that, mostly just an estimate. Far as toys go, can always check a store like goodwill, they tend to have cheap stuffed animals for the dog to chew on. Might want to be careful about what the toy is stuffed with, can squeeze it to get a good idea, try to avoid toys stuffed with bead filling stuff. Regular fuzz is generally fine, though it's a good idea to get it away from the dog if possible since they can't process it when they need to go out.
2.) 3 or so is probably fine. Morning, noonish, and evening tend to be good times, if the dog acts like it needs to go it wouldn't hurt to walk it of course. I'd think males tend to be a bit easier to catch this on than females since males will generally circle around before doing something, females just tend to squat on the spot. From walking the pugs, I'd say maybe 8 or so minutes is good, they tend to be ready to go in by then.
3.) Mostly done outside, paper training is an option too of course, but I can't really comment on it since it's been a while since I paper trained a dog.
4.) Some dogs are pretty clingy, pugs come to mind again, from what I've seen they generally mope while no one is around to give them attention but become really excited when their owner comes home.
In the case of pugs, don't expect to have much personal space any more since they will gladly push themselves in so you have the privilege of paying attention to them. That said, some like to play and others just like to spend time with you, varies from dog to dog.
5.) It's a pretty big responsibility, main things to do are making sure the dog gets enough water, gets fed, gets attention, and is walked/taken out when they need to go.
That should about wrap it up, nothing wrong with doing more research though. If there's a specific breed that catches your interest, pet stores tend to have books about the breed with more info.