If I upgrade to Go for a year can I go back to the Web version and still have access to models created in Go? Does Go provide the extension features and more tools?
With the Go subscription you sill not allowed to use desktop version, so you can not use extensions.
Go subscription includes the web based SU with some additional features on top of the free web version. (also you can use on iPad. )
See: https://help.sketchup.com/en/sketchup-web/sketchup-shop-frequently-asked-questions
With the Pro and/or Studio subscription you can use the desktop version as well as all above.
and: 3D Modeling Software Pricing – 3D Design Program Cost - SketchUp | SketchUp
Thank you!
Do you know how much cloud storage the Web version is allocated?
Yes, see in a first link above
10GB via Trimble Connect, Personal - for the free web version
Unlimited Storage via Trimble Connect, Business - for Go (and above) subscription
Thanks again!!