Have you tried the new Solarwinds MP? They updated it late last year and it seems to be pretty good. Of course I was getting an alert storm and had to uncheck several interfaces in the config wizard.
When you insert JSON into the Matrix tile, you should just be inserting the contents of the columns array (and the UI editor should give you feedback if what you’ve entered isn’t valid JSON, though it doesn’t check the schema).
Once the columns look good and function in the matrix tile, then you need to create a row perspective file on disk (see 34:58 in that webinar) which include the full contents you have above. As Jelly stated above if done correctly once you reload dashboard pack content (via the UI) or recycle the app pool, when creating a matrix tile and scoping to your object, you should see “Solarwinds Overview” listed as a perspective you could select, and if your rank is high enough it will be the selected default.
Worth noting btw - when configuring custom labels or row perspectives, Squared Up will lowercase the first letter of the property name. So you probably need {{properties.lastBoot}} etc.
I am currently updating the MP. Name schemas / pattern can be then configured via Overrides and devices that are just monitored via ICMP are been made visible, too.