Do they have bus to take you to this place?

Dc buses go everywhere. Just plan your trip on google maps.

There are 2 entrances but both are not always open all day. Look at website or FB page before going, especially if taking bus or taxi, Uber or Lyft.

Public transportation

The B2 stop is two blocks away from there

Yes

I have no idea, i know that there is one passing by Bladensburg Rd but don't know the bus route

No. You can take Lyft or Uber. That's what I did without a problem.