Already implemented

Yes, multiple instances of CintaNotes can work with the same notebook. Since CN uses SQLite, all DB interaction is done within a transaction.
I have taken the liberty of converting your points into separate requests:
http://roadmap.cintanotes.com/topic/87250-shortcut-to-run-second-cn-instance-on-the-same-database/
http://roadmap.cintanotes.com/topic/87251-different-titlesicons-for-different-cn-instances/

This is already on the roadmap as a different suggestion here: http://roadmap.cintanotes.com/topic/15284-saved-predefined-searches/