I'd be really surprised if they needed more than the smallest package.
I have a personal site with (I estimate, just from doing a "properties" view on my local folders) over 2500 files (including documents, scripts, images - everything) on the smallest package. The site has a blog, our family site, my husband's Land Rover site (

) and a bunch of subdirectory subject matter in the family site - akin to articles, I guess.
I've got another 15 MB of disk space, and my bandwidth use is small. I get about 400 +/- pageviews a day. My busiest day recently, with 1500 pageviews, was 0.0181 GB used.
I always install the bandwidth script
discussed here. Makes it easy to keep a daily eye on bandwidth.
Just educate the client about the possibility of needing to pay for more resources in the future. If they get so busy they need a bigger package, that's a GOOD thing!