Welcome to the community, Stephanie! Questions about running a photography business are welcome and on topic here, but questions about using photographs in your marketing model are usually a better fit for expertise elsewhere.
In your case, you need to explore a couple of topics in other places:
- Copyright: You should speak with an attorney in your local area so that you understand exactly what your photo submission site's terms and conditions should say. It's a risk to your business to use a submitted photo to promote your business without any sort of legalese protecting you. I can't promote this enough: speak with an attorney!
- Marketing/Design: Speak with marketing and web design experts for the layout and wording of your promotion. Search for other businesses doing the same thing for additional ideas.
- Web Development: Yes, it is possible to have the photo streamed to your facebook page and to have a person tagged. There may be Out-Of-The-Box apps that do this for you, or you may need to hire a web developer to build this functionality into your site. Either way, you need to seek a Web Dev for insight.
Web Development & Design: It's possible that the above two bullets can be found within the same agency.
Should you ever have a question about producing photographs - you've found a good place for that.
