Maybe i can help ya!
Ok for the ears, there are lots of tutorials on deviantart and on the web in general that could help you. I even found one that are headband-less and just fit on your own ears!
Here's the link: Bandless Fox Ear Tutorial
For the tail, you could just follow on or both of these sites' tutorials:
Wolfden's Tail tutorial
When it comes to the fur collar, well, what I would do is find a neck pillow that is white or something and maybe attach some white fur to that? I haven't really tried doing this, but it sounds reasonable enough! Remember, I'm just giving you some ideas that I have on hand at the moment.
I hope this helps ya! Oh, and good luck fellow Eevee!
IDEAS FOR FUTURE COSPLAYS!!!!
---Vaporeon full body suit(Pokemon)--10%(planning)
Deadline: Matsuricon 2012 (August 24th-26th)
---Toothless quad suit (How to train your dragon)--0%(TBA)
---Ezio's Armor of Altair outfit (Assassin's creed 2 and Brotherhood)--0%(TBA)