Hi ,

For texture editing:
UV Toolkit² - https://extensions.sketchup.com/sv/content/uv-toolkit%C2%B2
SketchUV - https://extensions.sketchup.com/ru/content/sketchuv

Rendering:
Corona Renderer- You can test out, it's in Beta phase right now. Please read through this thread: https://corona-renderer.com/forum/index.php?topic=14591.0
Visualizer - http://www.getvisualizer.com/

Joins?: (Not sure but maybe this article or plugin help)
Making components that animate https://help.sketchup.com/en/article/116822
SketchyPhysics - http://sketchucation.com/forums/viewtopic.php?p=536443

You could also take a look at Indigo which can be used free for non-commercial work, renders are then limited to 0.7MP and has the Indigo watermark.