Thinking of building a SW company using open source

We are thinking of using an opensource core to expedite a SAAS offering we are building.

Why? We think this will save us about 10 man-years of work.

We plan to use an opensource app and heavily modify it. In the end we estimate that final product will have around 30% of opensource code.

- throw away the entire front end, i.e, build brand new user interface

- build new APIs

- Modify the core functionality quite a bit.

The platform we are considering is MPL 1.0

We do not plan to offer the Source Code - it will be entirely cloud based.

Questions: 1. Has anyone built such a product? 2. Can i still get funded by VCs (we have angel investors now)

Thanks