I am only theorizing that the reason they went to so many different Walmarts is to help avoid detection. Let me know if you can think of a different reason to do this.
You pointed out an interesting fact, that by going store to store to store, it only draws scrutiny and makes them look like they are doing something suspicious.
If they were shopping for anything to facilitate their crimes in any way, then why bounce around from Walmart to Walmart? Why not, like you said, set up an online anonymous account or at least go out of state to more obscure stores?
The fact that there is no DNA from GW4, leads me to suspect his will be a circumstantial case. In other words, there will need to be overwhelming evidence of the things he did before and after April 22, 2016.
The exception being if they can tie the gun silencer or parts to make a silencer to him.
Amateurs don't think enough about the evidence they leave before they commit a crime. They are worried about evidence at the crime scene and getting rid of their clothes and weapons after the crime etc...
Jake's DNA will be all over the 2 Rhoden homes he shared with Hanna so it's a moot point unless his DNA is on the victims or on a weapon or on other obvious things from that night.
Sorry, I'm getting off subject, just speculating....