Never mind the FA50/1.4, if you've got the cash, then most definitely the FA43/1.9 Ltd--solid metal construction and very nice IQ. If you don't have the cash, then the FA50 is still an excellent lens, in it's own right, though.
I noticed that in your sig that you don't have anything on the longer end past 80mm. There are several decent choices in affordable telezooms (under $400 new); my top pick is the DA55-300, which comes in at around $300 new. If you don't need as much reach, then either the DA50-200 or F70-210 are good, affordable choices.
As for your 18-55, it's a pretty decent lens for the money, so it won't hurt to keep it around for a while until you get a little more experience under your belt as to whether you prefer primes or zooms.
If you want to explore primes more, and you're interested in macro/closeup work, then the DA35 or DFA100 lenses are both excellent choices.
HTH,
Heather