Welcome M2Fam
Poles: They are "temporary", they run power to the new ttc station. Hopefully they will go underground once that project wraps up... sometime in 2017 (lol)
Noise: I live on the 5th floor, south facing. During the day there is some street noise but if you keep your windows closed you won't hear a thing. Usually by 7pm it calms down, however, as someone else mentioned the only nuisance is the odd gas tanker truck or when the airport is testing planes. That said, if you are a light sleeper (like my wife) you'll likely close your window at night.
Den: you should be able to put a wall with a door on the den and you should be able to use your own contractor. You may want to check who the building uses though, as you may get a better rate from them. Kitty at the management office can help you, she's super helpful.
Hydro: I'm not sure how people are spending $40/month on hydro, my wife and I only do laundry/use the washing machine after 7PM and on weekends and all of our appliances/electronics are energy star and our spring/summer hydro bill hovers around $70 and fall/winter is closer to $80-85. For example, my most recent bill was $71 and we haven't been running the heat for 2 weeks.