SO... I know this is going to make me sound like a party pooper but it is 100% never a good idea to start off with a Kickstarter right off the bat. Kickstarters require a lot of planning ahead, publicity, communication, and hyping up in order to be successful. In the VN community I'm a part of, some people plan for their Kickstarters a year --sometimes two -- in advance, since the campaigns are all or nothing. So unless you're super popular (typically a few thousand followers) a Kickstarter is probably a risk you wouldn't want to take.
That doesn't mean there aren't alternatives, though! You can set up a pre-order purchase on Big Cartel or Storenvy so that people can "purchase" the charms and you can use those purchases to determine how much stock you will need to order. Typically, you would want to do this after you've ordered at least one proof from the manufacturer so your customers can see the product they will be ordering and have more confidence that they will receive their item. This method also has it's own risks, such as people getting refunds before the pre-order period is over, and having to ensure you'll be able to ship your items out within a trusting amount of time.
Still, the big part to making sales is advertising -- make sure you are publically talking about the merch you're in the process of making, use hashtags, post everywhere you can and always mention that if people want to know when pre-orders are open that they should follow you for updates. You may even want to offer a mailing list to email everyone when your pre-orders are ready. It's daunting, but so long as you use your time to wisely advertise your work and your intentions to create merch you can do it!