I have a personal account with Kasikorn. I would now like to setup a business bank account for a startup. What do I need to do this? The business will operate as a sole trader or maybe a partnership with my Thai wife.

Need to bring the business incorporation papers with government stamp, a official-looking motion of your Board of Directors moving and approving a motion to open account at that specific bank and naming the signatories on the account sealed with company stamp, your own documents. Usual paper shuffling but should be little problem.