I am creating a crowdfunding platform with a thousands of pages connected with a database. I am outsourcing it to web devs.
Price quotations received is about the same. Which language is good for scalability (lots of pages), has a big community (for support) and will be good to build a startup (building a team in the future)?
Focus on the team that will build the web platform, not the programming language. Choose a team that will be able to:
1) Understand the requirements
2) Build the product
3) Support you (this is the most important)
Seems that your budget is quite limited. If you do not spend your initial money wisely, then you'll spend way more for fixing and expanding the platform. Work with a team with a proven portfolio and proven experience. Look at their portfolios and their clients. Consider south-eastern Europe companies, too.
As a technical note, do not choose WordPress for such a purpose, as it does not scale up efficiently. Anything else from what you proposed is fine.
PHP has the largest developer community, however, also consider ASP.NET or Java, which are backed by huge companies. Facebook is not using PHP. It uses a private version of PHP which compiles to C++.