NW2010DB.mdf database is about 70GB large while WSS_Content DB is about 100GB. Is that OK? I cannot access NW2010DB via SQL Management Studio to manage. Can I somehow shrink it?
Let me rephrase. The database size is functionally OK, but I would have issues with it as an admin. It's size effects backup performance, and also could potentially be backing up stale data that is of no use. Thus purging year old data could be helpful.
Also, in a governance perspective, keeping the database size low for any database has obvious benefits it its physical capacity on disc. You are already experiencing issues with SQL management studio and you would never want the drive to reach capacity. And creating multiple Nintex content databases can help with management per site collection as some need longer historical data and some do not. So databases can be at different sizes on purpose.
So its OK, but I would personally want to look into shrinking it.
I wouldn't think that is OK and you should not have much trouble shrinking it down. But to do so you should follow the steps here Purge Workflow Data - Reduce the size of the workflow progress database table
There are several possible ways of preventing quick growth in your fresh database. You could create a Nintex database per site collection, and be careful of action use. Such as, do not have several log to history list actions in every production workflow. Use it when absolutely necessary, but if you have workflows that you needed to debug, but now ready for prime time, remove or disable those actions. You would be surprised just how much it could reduce the amount of history stored.
Retrieving data ...