It wouldn't technically be open source if it was a binary, but it would be freely-licensed.

I think the more important file is the fontforge one. As this is the thing people can edit and build upon. (the "source")

The otf, ttf and woff are just a bonus for people who don't want to install fontforge and and go through the process of exporting it themselves.

Ultimately it's your decision what you release. It's a similar concept whether you share a cake, or a recipe for a cake. The free software / open-source movement is concerned with sharing the recipes. That's why they share source code and files in the format they've edited it in. (And often include instructions on how to build it, since that is usually a bit more complicated with software.) It enables people to also load it in their editors and customize it, adapt it to their use-cases and fix issues.

You can also just publish the end-result, which are the otf and ttf files in your case. But people can't really modify or customize those. It'd be called a freeware font, then. It'd help people who just want to use it, but doesn't provide much more.

I'd invite you to upload both the sfd and the resulting otf and ttf. Usually that's how people do it. Distributing digital files comes at practically no cost. On the internet you can share a recipe and the actual cake alongside at no extra cost.