Advice on choosing a CMS

At the moment we have a online store on CMS OC project is developing rapidly. Currently, we are developing a new website, invested large resources of the company. The question is what CMS system to choose for a major THEM for long-term work, what parameters are important:
1) Important flexibility of the CMS, the possibility of deep customization
2) it is Important to have a large number of highly qualified specialists – razrabotchikom
3) support CMS
4) Continuous development of CMS/ obnovleniya
5) the Functionality of CMS/the speed and smoothness of operation

Question:
Should we, like CMS or to start developing a website from scratch ?
How to work with the developers (programmers), to hire or is , to control the quality of the layout, architecture to make the code understandable to other developers?