I've spent too much time watching people spend months and tens of thousands trying to bend 12 different third party tools together when a developer could do the whole thing in a week and it would actually do what you want it to do.

Nailing down the actual requirements is the hard part of building your own dashboard, it sounds like you've done that. If your needs are stable-ish or you have consistent developer resources it's going to be hard to find a better fit than that.

Actually, the plumbing isn't as difficult as most people make it out to be. Nowadays, its the era of abstraction and FOSS infrastructure tools like jQuery, Bootstrap and like you mentioned, Highcharts. I'm a freelancer who quite recently developed a Tableau replacement for one of my clients. This client realized that all he basically wanted from tableau was a chart and some basic data manipulation like sorting, filtering and grouping (count, sum, average, etc.). All the things needed to develop this little app already existed in the FOSS world:

1. Highcharts/jqplot for charting.

2. Twitter-Bootstrap for showing a professional front-page and UI elements.

3. jQuery and jQuery-ui for DOM manipulation, AJAX handling for SQL queries, enabling drag/drop, etc.

4. PHP/Mysql on the backend (which is needed in anycase).

As for plumbing, each of these tools is so well-documented and also a simple Google search will point to tons of StackOverflow links that happily provide an answer to any and every question you may have!

tldr; Library/Framework plumbing might seem complex initially, but for a practiced Web-Developer, its like a cake-walk!