web development framework - Javascript

Hi, am about to begin a startup web development project and looking at the wealth of Javascript frameworks and APIs ... its daunting and  overwhelming. Am coming from C# and .NET development background last couple of years ... the last time I delved with web development was 8 years ago with basic php, python and core Javascript only.

So some basic questions for those with recent web development experience:
1. build systems - grunt or gulp?
2. is bootstrap still the best frontend page dev for multiple devices ?
3. Sass or Less??
4. framework - backbone, angular, react or ember?? do I even need one?
5. need for dependency management (i.e. browserify)??
6. why node.js?
7. mongoDB vs MySQL?
8. best IDE for all the above javascript web development?

Thanks so much.