I believe there is no "replay" option on the official Roku USB Media Player channel. IIRC though, the private channel "USB Media Browser" by Nowhereman can let you play the videos continuously/repeatedly by pressing the “PLAY” button instead of the “OK” button when playing a video from the same folder. I think the only limitation is that it will only play the videos from a single folder, so if you put your videos in different folders and want them all to be player, then you can easily transfer them to one single folder.
This is actually a good idea, the thing is that the roku will have to buffer the next video file before playing it – so in between the videos you’ll probably have a short pause/time for the video to buffer. This may or may not work for what you’re planning but it’s up to you to check that. Anyway, the private channel code for the "USB Media Browser" by Nowhereman is KGULU.