Rehearsal Dinner Invite question

Hey girls! I have some questions about this:

1. Are they neccessary?
2. Where do you get them if you want them printed up? Is vistaprint a good idea, or is that only if you are adding a photo?
3. We only need like 15 invitations? Should we just get walmart invites? LOL! We are totally lost when it comes to this so any advice or info you may have would be SUPER helpful! Thanks!

I was in a wedding in Nov, where they hand wrote standard invites.

I wish I could be of more help, but I'm not even sure what I'm doing yet either