If I may make a suggestion for ads.
Have the adfly pages pop up for unlogged-in users whenever they download a theme instead of randomly when switching pages. Another option would be to have a banner ad loaded at the bottom of the page.
Ads might be annoying, but you are providing a free service and free content. I think it's reasonable to have an ad pop up when an unregistered user goes to download that content.
Also, a lot of people you ad blockers nowadays. You might want to look into getting onto adbock plus' whitelist if you decide on using banner ads. They have a few guidelines you have to follow, but the majority of their users would see your ads and generate revenue since their whitelist is enabled by default.
https://adblockplus.org/en/acceptable-ads