if you go to http://bulbapedia.bulbagarden.net/wiki/Trophy_Garden it will tell you all the Pokemon you can find in the garden
No they appear randomly
The Trophy Garden in Pokemon Diamond is located behind the Pokemon Mansion on Route 212. Many rare Pokemon may be encountered and caught only in the Trophy Garden.
No, you must have the National Pokedex to see Eevee in the Trophy Garden. Once you receive it, you can talk to Backlot and he will tell you which special pokemon showed up in the garden that morning. At some point, he will tell you that he saw an Eevee in the garden, then you can go into the garden and find Eevee.
You can find them wild by Pal Park, down and to the left of sandgem, or catch a bonsly as a special Pokemon in the trophy garden
In Hearthome
trophy garden
in the trophy garden
eevee
In the Trophy Garden
you get it at trophy garden
by hearthome city
trophy garden.