That luke helmet is not a correct
it looks like someone drilled out the innards of a regular stormtrooper head.
I agree. The bottom looks way too rough, the shape isn't quite right, and inside the helmet you should see an ejector pin mark (a very small circle from where a pin pushes the part off the die).
No idea what that red cape is from.
Not all weapons float. I hate the float test personally, as too many people assume a sinker is a repro, and I'm sure many legit accessories have been tossed as a result. I wouldn't worry about helmets at all - I think the Luke Stormtrooper is the only one reproduced out there. We know the R2 saber is a repro from the paint chip we saw, but there are legit ones that sink, as with some original sabers too.
Experience is your best bet, as with time, you'll be able to tell a repro mostly just from looking at it, but it takes a while to get there. Until you're comfortable with it, it's studying the minutia on TIG, or posting good pics here and asking.
Best of luck. Even if they were all repro weapons (and many are certainly legit), you'd still have quite a valuable lot there.