I'm so sorry about your loss, I couldn't imagine being a "witness" to that, i too would have nightmares!
As far as "how long" before you get another one...that's a personal decision and how YOU feel.

I lost my Julz in Oct and i was hoping i could make it to Spring before we got another one b/c we travel alot.
I've started my search on breeders back when Julz got sick and did alot of homeowork (about 2mo in my search).
The void Julz left our souls back in Oct, became so unbearable for us, that the "when to get another one feeling" was about 4 weeks after we put her to rest.
Dudley is such a lifesaver for us, he made our house feel like home the very same day we brought him through the front door.
There isn't a day that goes by that i don't think about Julz and cry for her, she will always be with us.
Dudley and Julz are so opposite but yet so identical....
I wish there was an answer for you but you have to feel it inside.
Sending hugs your way and that you soon heal...