@alan-wood,
In reviewing with the team, looks like there is another path forward regarding original bullet #3
Add an Idp (you could use google for instance)
Add a consent from settings > consents
Add a form field referencing this consent
Make an advanced registration form
Add previously created form field/consent to this form
Create a new theme (or extend your existing non-default/shipped theme)
Modify the theme to remove the display of the username and password in FreeMarker
Navigate to customizations > themes > all affected templates (in my case, this was the OAuth register template)
Here is the simple Freemarker that I used to modify (disclaiming now that you may want to rework this code a bit -- example only)
              [#-- Begin Self Service Custom Registration Form Steps --]
              [#if fields?has_content]
                <fieldset>
                    [#list fields as field]
                        [#if field.key == "user.username"]
                        [#elseif field.key == "user.password"]
                        [#else]
                            [@helpers.customField field field.key field?is_first?then(true, false) field.key /]
                            [#if field.confirm]
                                [@helpers.customField field "confirm.${field.key}" false "[confirm]${field.key}" /]
                            [/#if]
                        [/#if]
                    [/#list]
                </fieldset>
                <div class="form-row">
                    [#if step == totalSteps]
                        [@helpers.button icon="key" text=theme.message('register')/]
                    [#else]
                        [@helpers.button icon="arrow-right" text="Next"/]
                    [/#if]
                </div>
              [#-- End Custom Self Service Registration Form Steps --]
Now when I see my register page, I get view like this.  The Idp that you select will use the hidden username/email and password fields.
You are going to want to also customize the label for the consent.  More information can be found below.
https://fusionauth.io/docs/v1/tech/guides/advanced-registration-forms/#consents
804d24ad-6884-411f-812e-85cb26406b7b-image.png
⬇ ⬇ ⬇
1b22fb15-8544-4b19-a267-54aeea3236ad-image.png
Does that require completely replacing the UX flow you have with my own hosted one?
Yes, I believe that you would have to do this to add your own pages.