integrating my various business processes into one website

I own a chain of retail IT/Computer hardware shops across Karnataka,India. I use different softwares for my business processes namely accounting,inquiry management,customer service/support, sales team management and inventory management. All the applications are windows based and i need to buy a licence for every software per store that i own. This has increased my dependebility on windows and has increased my operating costs due to properitory software. The problem statement is as explained above very briefly. I need a webbased solution to automate all my business processes which will also enable me to eliminate microsoft windows from my organization hence reducing my operating cost. all the technlogies used have to be open source and commercially free. i will be happy to receieve your bids as the project is challenging and requires expertise of the highest levels. I can negotiate on the amount given the project is completed as per our needs.I will be assisting you all the way through the development process as i am a Computer Science graduate B.E too.