MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
80-90 grams works for most people.
If you have higher friction bearings and/or unbalanced spools, you might need up to 100 grams.
With very good bearings, you can get 100% functionality with only 65 grams.
Your existing nuts/bolts should work, but are on the low end of the "known good" range.
I would probably buy the longer bolts and additional nuts as insurance if they are reasonably priced.