Star Ocean is a great series, and if you're thinking about getting into it, stop thinking and start doing! The PSP remakes are solid games, and The Last Hope has a better battle system than any Tales game, in my opinion - it's real-time combat at its finest. Till the End of Time is...an acquired taste. I never acquired a taste for it, personally.
I'd recommend giving The Last Hope a try if you're looking to play the series, at least for the moment. Second Evolution was recently re-released on PS Vita and PS4 in Japan, so I expect it'll come here eventually (it had bloody well better!) and I expect Till the End of Time will be re-released as a PS4 classic. First Departure will hopefully get the same treatment as Second Evolution, leaving The Last Hope as the odd-one out, aha. It's a pretty good game in its own right, although a couple of the characters are infuriating (which ones depends on who you ask; I'd say Meracle and Myuria) and the plot stalls in a couple of places.