Hmmm, I'd be careful about attaching a porch slab to the home ESPECIALLY if the ground it 'sits' on is sloping. I'd have a different opinion (I think) if the ground was flat (but I can't see it from here.) That slab could pull your foundation out. My porch runs the full lenght of the front of the house. It slopes on all 3 sides 'away' from the porch. (It was built 20+ years ago but) It's split in the middle and one half 'dropped' 4" and the other half seems to have not moved. Erosion on one side seems to have 'assisted' in causing my problem. The only way to fix it is to have a new porch poured. (Forget that - It's not that 'critical'.) Had the porch been attached to the house, it might have pulled the 3 step w/it as well as caused the foundation to crack. Unless you can get the surrounding ground, about 3' on ALL sides of the new porch, I wouldn't attach it. Even if you properly graded. That much weight will move in more than the 'down direction', if you know what I mean.
It's best for the ground to be flat when the porch is laid, THEN you grade it. You see, if the porch sloping part of the grade NEVER slopes below the base of the new porch, then the only way the porch will go is DOWN. And that's what you want. So, level the area where the porch will go adding 3' to ALL sides, THEN dig for however the Pro wants to do it. And when the concrete is dry, THEN grade around it. (See what I mean?)
As for the method of doing what you want, I'd go w/the 2nd Pro's suggestion. If you can see what he's doing, he's trying to get the footing BELOW and DEEP enough so it won't move. If you can do this, you don't need to attach the porch to the house. Others may have some input so stick around.
My best to ya and hope this helps.
Jay J -Moderator