I was pointing out the excessive costs you could run into trying to build a gun. I suggest you go with the trigger job and go out and play. If you get serious about competing and winning in IPSC, you will end up with a different gun sooner or later.
My Standard Division gun is a Bul M5 IPSC model, these are available from Marstar and I highly recommend them, the ones I've seen here in Australia have all been close to flawless, they come with race sights, magwell, safety catchs, mag release and guide rod already fitted.
http://www.marstar.ca/gf-BUL/M5-IPSC.shtm
The ultimate top of the range standard gun is the STI 2011, which will set you back more again.
http://www.stiguns.com/guns/Edge/Edge.html These are available from Freedom Ventures.
http://www.freedomventures.ca/sti2011.htm
Now assuming you still want to go with building your own gun, for sights either Bomar or LPA for a rear sight, Dawson Precision seems to be popular for a fibreoptic front sight. I'm not sure, but I believe you will have to have the slide machined to fit a new front sight.
Go with Brownells for parts, Freedom Ventures also stocks some parts:
http://www.freedomventures.ca/gunparts.htm
I'm not a machinist, so I can't recommend your best course of action as far as modifying your gun.