Are you familiar with VTK code to setup a renderwindow and the parameters needed to configure your transfer function along with the slices for the MPR part?
If so it might be easier to build something new using what the next version of ParaViewWeb has to offer for building new web app. The current limitation is that you will need either pip install vtk --dev or paraview/nightly.
My worry with Visualizer is (1) editing the old react code from the client side and (2) add needed python code on the server side for the MPR. Especially lot of the code is really designed to be “like paraview” with a single view.
The (2) is really not bad when you know ParaView as you just have to create other views and tune them to match your expectation using the python interface.
And in fact if you prefer to interact with ParaView you can use that python code on the server side with “ParaViewWeb (next)” as well.