#2
I don't think so. I use my first knuckle (the inside of course) of my right thumb, and it doesn't really hurt.

Don't take this as gospel, cause i'm normally a guitar player, but that's my experience with it'
If Rock is a lifestyle, then Metal's an addiction

"People don't kill people with giant boulders"
"They will if you take away their assault rifles"

Quote by Gee-tar-eist
I wouldnt give a ****, i would gladly play music for people to steal it!
#3
Nah...I've been playing bass for a long time and my thumb never really hurt. Granted slapping isn't my main style but when i got into it i never felt discomfort...except when i accidently hit my bridge....that blows. just feel it around and find the sweet spot on your bass.
#4
your thumb shouldn't end up hurting unless you slap really hard and go for a long time. however the fingers that you pop with (pointer and middle fingers) will hurt pretty bad when you first start out. like, really bad. I couldn't play slap for more than 15 minutes when i started. But now i can go for a long ass time before it starts to hurt.
Gear:

Basses:
2008 American Standard Fender Jazz
Ibanez SRX300
Amp(s):
Ashdown MAG 300 C410T + 1x15
Effects:
SansAmp 3-Channel Bass Driver D.I.
#5
Nah ive been working on a lot of songs with slapping for about a year now, and even in the beginning my thumb never hurt from it. Although i have gotten a blood blister from the finger i pop with after playing for a while.
]One Among The Fence