Buying a random pr 3 - 5 aged domain name vs a new domain.

hey guys, so i am about to launch a new webshop quite soon, and i've bought 5xpr3 domains with 1k+ backlinks and their are aged, 6xpr5 domains that are aged and with 1500 - 5k backlinks according to majestic seo. Now i am going to use these domains to build blog network with unique content, videos and images and backlink to my money site which is the webshop, on top of that i will order some seo work from someone on here, but is this even necessary having the quality in mind of the other links i will be getting from my own network? my top ranking competition only got a few hundred almost all of them from forum posts on a few same sites. Now here is the main question: should i buy a random aged pr 5 domain name and disregard the name of the domain for it to rank high and be able to work more agressively on it seo wise without getting a punished by google for it? or should i get a name like "mywebshop.com" instead which would then be a brand new pr 0 domain but probably be easier to understand for the customer? all help and insights is appreciated!

thank you!