Welcome to ECF, and yes, kits are often an advertised "thing" and some sites "offer the option" of adding in juice, batteries, coils and etc., but by no means do all sites do this, and even the ones that do, often, you will find that stuff "unbundled" as it were. Lots of great vendors to choose from you might look though the list of ECF approved vendors and that should give you a sense of how many and the variety of vendors that are out there. It can be nice to use an ECF supported vendor as they usually have a forum and if anything goes wrong along the way, it can be easier to get in touch with them.
Welcome and I hope you enjoy your stay here!
Anna