Hello and welcome! I can't answer #3... so I'll give my best at #1 and #2. Hopefully others will see this and answer where I can't. (Being only 22 going-on-23, I have yet to experience the baby seat thing.)
I've stood on my Escape's roof before. I'm 200+ pounds (kind of a fatty), and I obviously didn't stand in the middle of the roof... but more along the stronger points, like feet along the roof rails. My best estimate is that it's limited by the crossbars. The standard bars are pretty tough. We have a couple members who opted for the Thule setup (and maybe a few with the Yakima) who would probably know better.... so to answer your question, I think it's limited by the crossbars. But... how often are you going to be putting stuff heavier than 100 pounds on top of your car? Just curious.1. The factory roof rack supports 100lbs...if I buy some better cross-rails from Thule/Yakima can I increase this number, or is it actually limited by the Escape's roof?
You'd lose out on some rear ground clearance, but if you're not doing anything that would require it, then probably not. I can say that my OEM hitch might've saved me some extra trouble when I got low-speed rear-ended 2-3 months back by a Jeep Liberty because it kinda provides another crossbar in the rear. If you opt to get an Escape sans hitch package, you also don't get the wiring, but that's not a difficult modification to do later.2. The factory hitch is 1.25" and I would prefer to get a 3rd party 2" hitch...are there any reasons why I should not be doing this?