All other things being equal a general site link hierarchy should be visualized as a pyramid with anchors where top level pages support lower level ones. e.g. a top level "computer parts"
Supports 3 lower level pages
"used computer parts"
"new computer parts"
"refurbished computer parts"
The top level page is in return supported by having a link on every page (main nav) where lower level pages (by being far more specific) compete at a lesser degree and do not usually need much support to rank well.... where broader terms need all they can get.
You could also have another section (pyramid) as "computers" that follows the same design
e.g. a top level "computers"
Supports 3 lower level pages
"used computers"
"new computers"
"refurbished computers".
...and your titles, and text would add the on-page weight according to each page topic.
As to your second question: Sure why not! The fact that the moment you start - it isn't going to rank but you can get Googlebot there "as you build"... and the value of this is "catch the fresh wave" or a bump up every few days in results as Google find new and rapidly changing page content.
CAVEAT on this: "be sure that your level of development is fairly rapid" - as there is nothing worse for a new website than getting exposure well before it's ready.
With a little practice you can have the final touches in place and have it ranked top the next or same day.
