i am a huge supporter of do-it-yourself, so i would recommend going with building your own unit, this way, you know exactly what everything does, where it goes, and how to fix it when it blows up
one of the things that i am curious about though is your reason for going with the pico psu, and the dell inverter(though you are correct that you need more than just the pico psu in the car environment). why not just go with a m2/m3 mpower supply?
i think i have the amp that you are looking at, and it works fine for me(i can never remember the model number, but it is a 300wattx4channel amp). though i did need some preamps to get a decent audio level into the amp(though, i am also using a external sound card, so it could be that too)
for the screens, i have a 619, and havn't have any issues that others are having, and have also read about others with the 701, it seems that there might have been some issues with a couple, but overall, they are decent screens.