If you have a complicated mechanism like that, building this in a CAD-Software and exporting it as Simscape Model is probably something I would recommend. To do this use the "Simscape Multibody Link" plugin for Inventor, Creo or Solidworks.
But what if you do not have access to those programs? Then building it like you do is still possible, but it is harder. What you have to have is a stationary assembly (like the drawings you provided), where all your points are known. This can be done in any CAD System or by calculating your positions (and angles) by hand. This is extemly important when working with parallel confugurations since the joint angles at the start of the simulation should give a valid configuration.
Then you can transform the positions accordingly and set the right joints, which you already did correctly (like for "boom point3" and "arm point1")
By your model I see that you probably have a position violation like this:
Error:['parts_model_analysis']: The following errors were found in the model parts_model_analysis.
Caused by:
['parts_model_analysis/Solver Configuration']: *** Model not assembled: position violation *** Resolve this issue in order to simulate the model.
This happens when your parallel connections do not line up in the first simulation step. That's why you need to bring the bucket and straps to the correct position/angle when configuring the model. Just read out the angle in you CAD-Program and rotate the bucket and staps accordingly.
PS: I think it would be better to use prismatic joints instad of cylindrical onces, since the cylindrical ones give you an extra degree of freedom, which you do not have in a real excavator. But not changing that should easily work.
Also you set the spring stiffness of the cylindrical joint. Not quit sure if you really want to do that since normally there is no Equilibrium Position on a hydraulic acuator which gets enforced by a spring (I think).
