Sibelius First is a scaled down version of Sibelius. While it provides a great way for people to get started with all Sibelius has to offer, it will not be a good choice for Virtual Drumline users.
It doesn't support custom percussion mappings and staff types that are important for VDL instruments to display properly in a score. Even though it supports AU/VST plugins, the lack of control over percussion mappings won't make it very effective in properly interfacing with VDL templates which allow users to display notes one way in the score, while ensuring notes play back a desired sound.
If you're just getting started, and want to use Sibelius notation software with Virtual Drumline, the full version of Sibelius is the way to go. They do offer discounts for students and teachers which are marked down considerably from the full version.
You may download a demo copy of Sibelius from their website here.