Change or upgrade our old MAGENTO web shop and make it multichannel EBAY & AMAZON compatible

Hi Freelancers, we have an project to be done on our current web page. We have had in the past some projects on freelancers and had sometimes troubles with empty promises and lost some money, therefore we can't accept any prepayments, partial payments or whatever similar. We are a serious company, working already 10 years in our field and do fulfill our part always and search only serious freelancers. All them who ask for a prepayment we will not take into account. Now to the project, our web shop is made in MAGENTO, 4 years old and has several customized modules. Whenever we want make re indexing or upgrade we have problems so we decided now whether to move to another system or upgrade it and use only Magento own modules. In the attached file is the description what need to be done, and what change's we expect. The deadline of our job is 25.09.2015. Until this time all should work's on a copy of new page which might be uploaded into our server. The guarantee for the new upgraded web shop and its' functions shall be not shorter than 6 month, where we expect a support and 24h reaction or 48h solving of any trouble.