WordPress.com is 100% free to use but there many premium features that you may consider purchasing. Probably the most nessesary is a Custom Domains. Without this upgrade your domain will be yoursite.wordpress.com. This is fine for a for a hobbiest or temporary website. If your needing to draw a lot of traffic you need a custom domain. You may buy domain a domain from WordPress.com or purchase it somewhere else. If you buy the domain from Godaddy or others you will still need to pay for domain mapping, $13.
VideoPress is an upgrade that enables you to upload unlimited videos to your site with unlimited bandwidth toget those videos to views.
There are several upgrade packages like the WordPress.com Premium package that give you a Custom Domain, VideoPress, Custom Design, No Ads and an extra 10GB of storage space will give you ample room for images, audio and video.
Do you need these upgrades that would depend on the demands of the project and how much money you have. I recommend the Custom Domain upgrade for sure but I will show you how to get around the rest.