Depends on what you consider better. Iron heads are thermally more efficient, so if set up identically to a set of aluminum heads they will make a little more power, but the extra compression you can run with aluminum heads makes up for that. Iron heads are cheaper, don't tend to blow headgaskets as much, but aluminum heads are MUUCH cheaper to repair, are lighter, and can help with overheating problems.

You'll save about 40 lbs.

Compression depends on deck height, gasket thickness, and combustion chamber volume. Type of material of the head has nothing to do with it.

With the size cam you want, probably so. You need to check your cranking pressure though. Get a cylinder pressure guage, screw it in, bump the engine over, and make sure you're not going over about 210 psi with aluminum heads, and about 195 with iron.

A Comp Cams Magnum 270 (for example) is about as big as you want to go with a stock stall. I wouldn't suggest going with anything over a 282 or so (about 234 duration at .050 on the intake I think) or you stand a chance of overcamming it. Best advice is to call the cam manufacturer and tell them which heads/intake/carb and what size engine you're running, what it will be used for, what rear-end ratio and stall you have, and what revs you will be turning (they'll probably ask you all that) and they will help you figure out which one you need. They're probably a lot more knowledgable than I am, so I'd call and ask them if I were you. Or at least ask someone smarter than me on here.