1. I use the Recycler Speed plugin. Will there be a conflict between these?
2. The way I understand it, you can configure this to pretty much prevent players from recycling something by setting the config to output the same item they inputted. Is this correct?

Hey! If you are still interested in exploring this plugin, the upcoming v2.0.0 release is currently undergoing beta testing. Please try out the beta and provide feedback if you are interested.

https://umod.org/community/recycle-manager/44014-recycle-manager-200-beta

To answer your questions:

1. This will probably conflict, but you don't need Recycler Speed if you are using this plugin. If you wish to use the Recycler Speed plugin anyway, you can disable the speed feature of this plugin in the config, when using v2.0.0.
2. With v2.0.0, to disallow recycling a specific item, you can simply add that item to the Restricted input items section of the config, and the item won't even be allowed to be placed in the recycler.