Your list is really good already. I particularly like the last one; If the stakeholders and product people are happy, chances are things are going well.
Other things you might consider would focus on the elements that differ between Scrum and Kanban.
How frequently do we need to make changes to priorities at short notice (if this happens a lot ...
Being a small team, take one project at a time
You said you want to embrace 'WIP limits' principle of Kanban among others. The reason why Kanban recommends WIP limits is to help the team focus and to minimize context switching. Instead you are flying very far in the opposite direction:
Use two boards in parallel? Create a 2D Kanban board? Embed one board
Open source software for Scrum/Kanban
Here are two open source options for software project manangement using Scrum/Kanban.
Tuleap ALM: See the Explore Tuleap Community Edition section for more details.
Taiga on-premise self-managed
You need to pay for the hosting provider.
You need in-house skills to install, operate and maintain these software.
I am assuming that the projects you are working on are small / medium Scrum projects.
Google spreadsheets or Excel Office 365 (to enable online collaboration) could be an alternatives.
You could google search for managing small/medium scrum projects using Google Spreadsheets templates(free) or MS Excel templates to be used with Office 365 for sharing(paid).
Just-in-Time (I wish people stopped saying Kanban) requires all tasks be of the same size. It doesn't matter which size it is (though usually smaller sized tasks are easier to manage & predict), but there must be only one. Otherwise you can't measure WIP limits in number of tasks, which in turn means you don't know how to balance the work across the ...