I used Dtac in the past for around 600+ THB a month.       I prefer to avoid contracts.

 

Anyone have anything to offer  about provider and data plan as well as price?   Fast, ample data, and etc?

You can use multisim option to share data with your phone. No need waste on another phone line since you will be using data only.

How "fast"  do you need for a tablet?

 

Unlimited data at 1 Mbps costs 321 baht. Unlimited 4 Mbps 535 baht.