I have an AC2350 Router and wish to attach USB portable Hard Drives to Router to play on Roku Media

The problem comes down to "i'm not savvy with that". 

Some roku's need a certain format to stream a downloaded movie because they don't have the CPU power to transcode. 

This isn't true of all of them but many do. So if you don't have your media in the proper format, they don't play. 

When you say "i'm not savvy with that", it makes me leary of the route you're taking. 

I'm sure we can add the drive and get it setup for you. Whether it'll work how you want is another matter. 

A better option might be for running a media platform like Plex or Emby. 

They scan the media, load photos of it, can handle transcoding if loaded on a decent enough computer, and tend to be a little smoother for home users. 

https://www.netgear.com/support/product/readyshare_usb_storage_access.aspx