I like hand-picking everything because that way you get to visualize different aquascaping possibilities as you're picking -- "Ooooh, I really like that big round piece and I can put the big flat piece right on top of it."
A few big pieces as a foundation with strategically placed smaller fill-in pieces will always look more natural IMO than a bunch of tiny stacked rubble. I looked at all of the past featured tanks on Advanced Aquarist for aquascaping ideas before I did my own tank.
I think the quality of life on the rock is ultimately more important than finding the exact right shapes. If your LFS has really good rock and a reasonable price then I'd suggest buying larger pieces at least from there and maybe supplementing with a case from online -- but that's just personal preference. I've seen lots of folks on the boards who were thrilled with their online purchases. Some people also advocate mixing and matching a bit from different sources to maximize diversity.
I bought my Marshall Island rock for my 90g uncured from the LFS and cured it directly in my tank (but didn't add any critters during this time, of course) while skimming, maintaining constant temperature and a reduced photoperiod... lots of stuff on the rock died during the ammonia and nitrite spikes, but i did daily 5% water changes and tons of good stuff lived and it cycled quickly. I'm now a month post-cure and I'm seeing halimeda and lots of other good macro algae, good bristle worms and brittle stars, and lots of pods and various sponges. I had a small reef tank briefly 5 years ago started with pre-cured live rock from the LFS and don't remember it being as densely populated.
Definitely keep the temp constant in your rubbermaids, skim and change the water if you go that route -- I don't believe lighting is the most critical piece of the puzzle while curing, it's more about temp and chemistry.