website for users to post advertisements and notices

Hi All, I need a website that enable user to post advertisement and notices. 1) It should be able to handle high traffic. 2) Sign In and Sign Out. 3) Must be optimized for search engine top 10 results for the keywords relevant to the services i'm offering and advertisements posted. (Google and Yahoo) 4) User sign up form. 5) User particulars to be stored in database. 6) Pictures uploaded by user to be auto resized to website specs. 7) Someone who is interested in the product and want to ask questions, he/she would be able to post message direct to the advertisement. Meaning, when a person click on the title, it will open a new page, in that new page, the interested party can post message but requires sign in. note: users don't have to sign in to view ad unless he/she wants to post message. 8) search capabilities 9) I would be able to include adsense to my page as well as my own advertisement banners. 10) The website should have back end. 11) Include modules and upgrade. 12) Should be able to add extra modules and upgrades. 13) Templates and Icons for the links. 14) banners design. *do include some advise and suggestion on layout and features u have in mind base on your experience. Can be done using your own script or website builder like soholaunch or mambo. Pls advise on pros and cons. Let me know your experience and other projects that you have accomplished and promoted. Also include how are your going to plan this project, a couple of proposed layout and by when the draft will be done and the overall website to be completed. Full payment after project has been completed. All payment via escrow. trustworthy and with a good intergrity and easy to be reach and communicate service provider please bid.