My presets from the original mod by Goalie are gone!

Unfortunately I see no way to get the old preset-info from Goalies version (or my previously fixed version from github).
This version of the mod has a unique name so the old data cannot be migrated.

Why does the mod complain that I need to open a target/source entity?

This is the new default behaviour with version 1.1.1/0.18.3 that came with the ability to copy presets from other entities than the player.
If you wish to restore the old behavior (use player if nothing else is opened) there is a setting for that.

How do I import blueprints that are stored in the library?

This does not work at the moment due to limitations in the factorio-api.
Workaround:
Copy(!) the blueprint/book into the player-inventory and import it from there.

Is there a dedicated Version for Factorio 1.0.0?

No. Factorio 1.0.0 loads mods that are written for Factorio 0.18.x just fine.
You can find the latest 0.18.x Version in the mod-portal ingame and use that.