It sounds as if you're participating in a "giveaway event". Your product must be unique and that if it's a product from someone else that you have the rights to give it away.

Todd's right about using an autoresponder in capturing names and addresses (and utilizing the double optin facility to stop you from being abused of spamming in the future). Don't overdo your download page with offers as now you have them on a list for further mailings.

With regard to an OTO, you need to have one that compliments the gift you're giving away ie in the same niche.

Neil