Keeping the forstner square with a hand drill isn't really a problem, as long as you watch the sides of the bit as it goes in.
You just have to keep the sides of the bit even all the way around, and you are square.
I've never been able to do that as effectively with a spade bit.
I've also never had a problem getting them through anything (MDO, Plywood, Dimensional Pine, Hardwood Laminate) with a 12v cordless.
As you said though, I'm not FORCING them through it, I let it cut it's way down.
As far as marking holes, I just use a combination square to draw lines parallel to the edge of the panel, and then mark the cross spots and drill on the +.