I typically consider cost and function when deciding what mods I want. Until you've fired the gun for a while, how would you know what modifications you should consider?
Do you want to change the spring because you heard it needs changing? Each persons experience involves individual factors. I would think after firing 500-1000 rounds the spring may not be much of a nuisance worthy of dropping some cash. But by then you will be sure that you wish to change.
By my 1000 rounds of steel Challenge I really felt that the front sight might be improved with a FO. I also knew that the Cajun Reach Lit is what I wanted. Trigger pull was no big deal. Mind you, I've noticed the more DA firing I do the my finger strength increased, Thus the pull becomes less consequence.