I agree with peled's advice of going to an Apple store to play with it before you make your final decision to get an iPad. They should have the whole iWork suite installed on all their iPads so you can try them out to your heart's content.
Keynote and Numbers received updates in the past months that allows them to export to microsoft .ppt and .xls files from within the apps, which was a much called for feature when they were initially released.
Also, to answer your question, yes Pages has Times New Roman as well as 39 other fonts to choose from.
I'm trying to use the iPad for at least a school year at college and I'm halfway there. I've written papers, reports, etc. using Pages with the on-screen keyboard and find it surprisingly easy to type on. There have been some slight formatting issues when exporting to Word docs from time to time, so I would try writing some things on an iPad in the store and emailing them to yourself at home as a word document to see how the formatting looks for whatever you want to write. Also I've seen similar small formatting issues when importing Word documents into Pages like sometimes removing paragraph formatting on import, but the app does a good job for the most part in resolving most formatting issues.
I've heard of issues with Numbers either not reading certain excel files or displaying the files wrong, but those complaining about it were use very large spreadsheet files (thousands of entries/cells). I doubt you would encounter this type of situation in a school type of setting.
What exactly are you thinking about doing with your iPad in school? If it mostly involves writing papers and doing research in the web, and you're also looking for a device to watch videos or play games, then I wouldn't rule out the iPad as a valid alternative to a laptop. It all comes down to what you're looking to do with it.