Maybe start a blog or website, along with an email dedicated for your business. Wix and weebly are ideal for this, along with tumblr, blogger, Facebook, instagram, deviantart, and pinterest. Start with a few, or one, of these websites. Usually for this kind of business, you should open "slots".
Since what you're doing is similar to commissions, you should open slots.
This allows for you to get requests, but not be overloaded with them. Especially if it's just you and your dad.
Or, if you're simply making cosplays on your own interest and selling them, a website or blog is more ideal (actually, I'd suggest weebly, tumblr, blogger, or a forum based website.)
Be sure to pace yourself with these projects. Rushing will only mean poor service and outfits. Also, try not to be harsh on yourself at all. You're not going to start off perfect, and with every mistake, you get a little better.
Good luck with your business! (Not that you'll need it, haha.)
I hope this helped!
PS it's good to have a PayPal for this, too!
