Do not zero-write or DBAN a SSD. The controller will make this a moot gesture. You need to use the Secure Erase function that tells the SSD to flush itself. This is available in Parted Magic, which is free.
Answer to second question: yes. Wiping anymore times would not do anything at all, and merely wastes time, energy, and increases wear on the motor and spinning plates.
Wanna bet Mikel?
one time is definitely not enough. Wipe it 4 times.
I would bet, but I don't know you, and can't claim it anyway. So, here are the links (note, this is simply from googling "wiping hard disks more than once", so minimum chance of confirmation bias):