If I make custom-made cakes, will I have to pay any taxes as a business or collect sales Tax? ?

You'd have to pay income tax and self-employment tax.

Yes, you have to pay taxes on income, like everyone else.  Sales tax is a state specific question.

Being a minor doesn't matter.  You will have to pay taxes on your net income (what you charge minus your expenses).  You'll have to check with your state tax dept. to see if they are subject to sales tax or just ask at your local grocery store.  You will also need to check with your county health department to see if there are any regulations that prohibit you selling food products made in a home kitchen.

You are probably not allowed to bake cakes for sale without a health dept permit.

You probably don't get a health dept permit for home based baking.

You will have to research the health dept regulations in your area, including any cottage industry options (which are geared towards home based food businesses). 

Yes.

You will collect sales tax from your customers and remit it to the state.    Groceries are sales-tax free, but a take-out cake is not.

You will owe federal self-employment tax on all profit over $400 in every calendar year.

100% of your profit is subject to federal income tax (which doesn't necessarily mean you will meet the threshold for owing any income tax...it depends on your entire income/tax situation).

You may owe Iowa state income tax and also any local or state excise taxes as well.

Nowhere is there a special law that says people who make custom-order cakes are free from all taxation.    Being self-employed comes with additional responsibility.

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