Not with the current OH architecture. If you hosted a separate server that included the images you could then add in some code to that server to generate commands or updates to OH through OH’s REST API. But by the time you have gone through all that much work, you may as well continue the effort and build your UI over on this separate server or adding a custom widget to HABPanel, though OP explicitly stated they don’t want to use HABPanel.
The problems you site would almost certainly be an issue as well, particularly in the phone apps.
I don’t think this can be accomplished with either of these bindings. Remember that the HTTP binding is basically just an HTTP client, not an HTTP server so it can’t host the image. Exec can run scripts or command line commands so I don’t see what it could be used for to implement this.
I’ll reiterate that OH is not of that world. Expecting the sorts of features necessary in that world like transactions, rollback, realtime performance, enforced order of processing, input verification and validation, etc. to be available in a Home Automation system like OH is unwarranted. The two are similar problem spaces but the two have vastly different requirements and vastly different consequences when something goes wrong.
You can’t do that. Time cron triggers are hard coded. You cannot dynamically change them at runtime.
What you can do is use a DateTime Item and schedule a Timer. But again we are stuck back on the problem that OH doesn’t support a scheduler nor does it have a Date/Time picker so this is awkward at best. See the Individual Alarm clock for each Day of week, with adjustable duration for a pretty comprehensive workaround for the lack of a scheduler. You probably don’t need something this complicated.
Is not really all that different from Java development all things considered. You have a much lower barrier to contributing to the code than a non-developer would. I do know getting the development environment up and running is a challenge in and of itself though.