Make sure to follow the 4-to-1 rule - for every 4’ of climb, the base should be 1’ from the wall.

You should be fine. Ideally, you’d tie the ladder off to something, or have the top extend 3’ above the surface it’s against (like if you’re using it to get to a roof). Obviously neither of those really apply here. I’m an electrician and we have to do stuff like this pretty often.

As for the strength of the wall around the windows, those should be framed in, meaning there are extra 2x4s around them. Try to extend the ladder higher than you need to be so you’re not on the very top of it and you’ll be alright