The trigger itself won't do much in terms of how it feels when it's pulled. If you get one with an overtravel stop you'll be able to change how much the trigger moves after the sear is tripped, and if you get one with 'wings' at the front of the bow behind the pad, you'll be able to adjust how much distance is needed before the sear is tripped.
I wouldn't look into changing out the hammer without doing the sear as well. The 1911 should be considered a gun where everything must be handfitted, unless purchased together already fitted (like Cylinder and Slide offerings).
To change out the sights, knock out the rear sight, and install the new rear one, centering the notch over the bore. For the staked front sight, this is the best guide I've found :
Trigger jobs
The only things necessary for the 1911 to function is a good mag, sights that you can use, and a trigger you can manage - and even the Taurus offerings with 8.75 pound gritty pulls are pretty dang managable.
If you've got any 1911 questions let me know. I competitively shoot one and carry one every day for self defense. I do all of my own modifications and repairs, as well as those on friends 1911's.