I would use gumroad or whatever is easiest/fastest to get it out there. Don't worry about fees and junk right away. Get your product available to sell and focus on selling it. Don't spend a lot of time on how you are going to process money and deliver the product. Focus on the sales. When you have $10,000 in sales and 1% margin starts being worth $100, you can spend a few hours maybe worrying about if gum road is the right choice. Even then, it's probably not worth worrying about.

Just sell things, enough things that it actually matters who you are using for processing. But, with 0 sales, you are doing 0 order processing so it doesn't matter.