Your diagram shows that RADIUS will be used. You can use the Filter-ID attribute to ask the Meraki kit to apply a specific group policy to the user. Group policy will allow you to apply different service levels.
When using a splash page with Radius, the radius server can specify the speed of the client's connection. This will allow the radius server to pass the limit down to the client automatically.
Maximum-Data-Rate-Upstream / Maximum-Data-Rate-Downstream:These are used to impose bandwidth limits, only used in Access-Accept packets. The values are the maximum rate in bits/second. See RFC 4679: vendor-specific (set Vendor-Id 3561). If these values are not present, Dashboard will use the Bandwidth limits that the user set on the Dashboard traffic shaping page as a default. If these values are set to '0', Dashboard will set the Bandwidth limit to unlimited.