Does is cost anything to get in?

For the rose garden, there is no charge. Walm into the center and walk through the glass doors opposite the street entrance and yiu take stairs down to access garden. There is a fee for the museum.

No, It doesn't cost anything to get in. Except you might want to bring some money just in case you want to go to the museum or buy something from the gift shop

Not to walk around the rose garden. That is free

How much to host a baby shower

No nothing

Yes but well worth it