Micaela,
A comment on your Question 2, I have observed that while you can lock users out through things like version edit dates and workflow completed status, a workspace admin can defeat these lockouts by importing, both from CSV and model to model. This makes life much simpler for the admin if you need temporarily to lock down a live model, to update actuals data for example, and then return it into the hands of a user community to carry on adding and updating from the point at which you locked them out. If I need to block out various months, however, I prepare a CSV upload file, delete the unwanted months from the file, and check the 'target items to clear prior to import' carefully before running the import:D
If you are making a direct input of data, typing in over the blue numbers, or cutting and pasting from a spreadsheet perhaps, even an admin is constrained by the version edit dates and workflow statuses.
Basically a small data set is quickly typed or copied/pasted in, workflow permitting, but a big one is more quickly done through a CSV file, so you have to estimate the balance before you decide which way to go.
Mark.