Quandry about ordering parts

Got my Dart back from the body shop, underhood rust repair and engine compartment paint, going through catalogs and websites and more confused than ever. One place sells some of it in kit form, some by the piece(such as firewall seals etc.). Do I order all my parts from one source, or do I order some parts from here and some from there based on price, as one part will be cheaper at one place but the next part will be cheaper at another place. I am looking at mainly paint gasket sets, battery tray, hood to cowl and hood to radiator seal, and trunk weatherstrip, and brake lines. Suspension and brake parts I will buy locally.
Thanks