Making my Classified advert site more dynamic before launch

A couple of years ago, I purchased a classified advert program for which I have been working on to create my site. The software is written using php, sql, css and jquery I believe and is set in a way that when I log in as an administrator, I can create categories, sub categories as well as custom fields for these categories. The software is quite dynamic and pretty neat but I have been requesting particular features for a long time now that I would like to see to best suit what I would like to see for my site but have only now been told I will need to find an external developer to make the modifications I require. At the moment, the program will only allow my users to place an advert in one category - I wish for them to be able to select more than one! I wish to integrate an advanced comment/feedback and star rating system as well as an advanced promotion system that are linked in a way that my customers can be rewarded for their time by gaining ad credits (this would require some sort of control and settings by me in the administrator control panel). In the current software, i create custom fields that a user can select/interact with when placing or searching for an advert but I wish to be able to make this more dynamic by the use of chained selects. for example: if i create a custom field called "Manufacturer" in the "Cars" category, I can set it so that a user has an option of manufacturers to choose from, but once selected, thats it....I can then create a list of models but the two would not be linked. I want to be able to set chained selects up so that once a "manufacturer" is chosen, a list of "models" appear to select from that are only relevant to that particular manufacturer!.....The system is there in the software to create good detailed adverts but the data created on the sql database surely could be sourced to do what I require? It is possible in the software to integrate paypal payments, so that users can sell individual items using their own paypal accounts, but I wish to give them the option to set up a shop if they wish to!....So an option to have a shopping trolley would be good?... I have a few people requested that when my site is launched, they are able to sell photographs and pictures....So what I would like setting up is a way that when a customer purchases a photo or picture, and payment is received - the download only then appears! Ideally, items should be watermarked so they cant be just copied! I wish for my users to be able to search adverts by setting a distance from their post/zip code...this would need setting up!... Another feature I would like to see is a "memory" feature in my forms....along with suggestions......As users type, I would like suggestions to appear based on the entry box use/website content. If someone begins to type something in a particular box.... suggestions appear, but if there are no suggestions relating to whats entered, the word(s) entered are saved/stored to appear in future suggestions (due to misspelling etc. it may be an idea for these to be saved temporarily in the database, lets say 60 days and only appear as a suggestion/option if more than ____amount of people enter it within that time period)....I hope this is possible!?....If so, it would be useful in advert creation if a particular type/model number etc of product is not listed, because it could be added by the user . Ideally, anything added should auto notify to admin!? I hope these things make sence!....it is really hard to explain without you viewing and understanding the site as it currently is first! I hope someone can help! If someone does take this job on, I would like to pay monthly if possible towards the total charge because I currently do not have access to large amounts of money in one go!