FUTO has many issues, beyond licensing like it's lack of privacy features.

Aurora store is a horrible placeabo. Not only is it using other folks anonymized accounts, which violates several privacy laws internationally it also still has the Google libraries in their apks like everything else. You are not gaining any privacy or security using Aurora Store or F Droid for that matter but are indeed opening up more attack surface in the supply chain that ends at your device.

GrapheneOS strongly recommends against F-Droid because it has major security deficiencies and adds an unnecessary middleman. Our recommendation is using developer builds of apps. F-Droid doesn't review the code for app updates but rather automatically fetches and builds it. They make questionable downstream changes introducing security vulnerabilities. The Accrescent app store provides developer builds of apps signed by the developers for everything included which can be verified. Play Store provides developer builds but only a subset of older apps are still signed by developers since they phased it out and heavily recommend switching to Play Signing.

Aurora Store is not recommended by GrapheneOS in general. Our recommendation is to use the sandboxed Play Store for installing apps when using sandboxed Google Play in a profile. We recommend only using Aurora Store for bypassing restrictions set by app developers on where their apps can be installed. That's what was said above. It would be better if the Play Store didn't do this.

Contrary to what you're saying, Android apps do not include Google Play libraries by default. They're only included if developers explicitly go out of the way to include them in order to use Google service APIs. Android SDK, etc. is open source as part of AOSP and both the OS and AndroidX libraries are open source too. The proprietary Play libraries are clearly marked as such via being in the GMS namespace.

With Grapheneos no need for developer options however. It's in the usual menu in the exploit protections submenus.

For the security preview channel where they have to withhold the code until it's officially released yes that comes out with/days after Google releases them publicly.

GrapheneOS has a security preview release channel that is opt-in but includes patches from these embargoed vulns already. Again, it's opt-in but for those with a higher threat model use-case it's nice to have.

Would this not defeat the purpose of responsible disclosure? As a bad actor I could learn of secret vulnerabilities from this channel.

You have google to blame. GrapheneOS tried very hard to make sure they have those security patches as google delays publishing the source tree and it's only available to OEMs

These patches are available to all vendors who chose not to protect their users yet.

Releasing binary patches is allowed, this is why GOS have added the security preview channel.