I would move this up to about the 3rd pick. Brown has a redraft ADP around 1.05, if you have the 6th pick in a keeper league I wouldn’t anticipate Brown being available unless everyone picking before you kept their 1st round pick.
I would expect at least a few of these guys to be kept with my estimated cost based on last season.
Gurley (2nd or 3rd round cost)
Kamara (late round cost)
David Johnson (1st round cost)
Zeke (1st round cost)
You could even throw Bell in there as a 1st round keeper. This would leave Brown as the next best player available in your draft. Without the first pick of the 1st round, Brown very unlikely to be available to snag if you kept someone other than Brown.
In the end, I would keep Brown. He’s a lock as a top 3 WR, and a good probability for the #1 WR most seasons.