RE: Inverted Circular Saw as a Table Saw?
Definitely doable.
There are comercially made tables just for this purpose - just like the tables you mount a router to the underside to use as a shaper. Works on the same principal - an inexpensive way to expand your tool options when you're on a low budget. If you can afford to have every tool out there (and have the shopspace to set them all up) go for the big bucks. If it's something you'll only use sporadically, this MIGHT be a viable option. Be careful with ANY tool - even the expensive ones.