custom coded website with shopping cart, automated emails and more

we organise different trade shows where there are multiple exhibitors who exhibit at our event and multiple buyers-importers & trade visitors etc who visit our exhibition. we want to build a website where our exhibitors can select from available booths, select extra furniture for their booth & other services that we provide related to the event. they will add everything to a shopping cart & a total invoice will be generated which they can pay online or later offline. there should be option to make partial payment or full payment. automated reminders if payments are pending. we should be able to setup different registration form for exhibitor, for buyer, visitor etc. these forms will have references, so an automated reference check mail through the platform itself. etc etc. admin should be able to upload exhibitor details aswell, their logos, contact details etc . presently we are using wordpress website but we will like to custom code based on our specific requirements, preferably in php etc. it will be easier working with someone who understands basic of trade shows atleast