It really depends. (Informative answer, I know).
On the one hand, doing the research and 'shopping' is most of the fun in preparing a new build. On the other, sometimes you don't have time or don't really need to do the research.
Buying a new PSU would take me 10 minutes. Building a new PC took 6 months .. but that was mostly waiting for the new Clarkdale CPUs to be released so I'd see what direction 1156 was moving in compared to 1366.
For my watercooling, it took about a week of research during down-time at work to come up with a preliminary plan and three back-up plans.
I'm going to watch this discussion because I suspect it belongs in a different folder. None of your examples, nor mine, have anything to do with modding. However, planning a mod takes considerably more effort than planning a build so I'll leave it here for now and see what the community does with your question.
yeah i wasn't sure where this goes but figured this was the best fit.