As far as I am aware there EA created levels will open in V1 without any problems, though with any new vesrion of an engine there may be slight updating you may have to make to enities and alike to accomodate the new version. I would not worry about the compatibility - TGC might like to confirm this though. 99.9% compatible I would say.
True Meleee and Water I dont think will have any extra support in V1 as I am waare - so you will have to fake, workaround, script or othrewise make those for yourself and get them to work best you can.
FPSC is not by deafult going to give you the best start if your game attatches major importance to those two features as they are poor or missing completely in FPSC. You best option is to get a copy of the demo version and see what tests you can get going to ascertain if you will be able to get FPSC to do what you want. Though you may already have done that?
What support there will be in future versions beyond V1 for the features you are looking for and how advanced they may be is anybodies guess. FPSC was never designed to support melee and it would be obviously harder to impliment than including more advanced water I would imagine.
Nice to see you hear Disturbing 13 - we have met on other Forums