I'm currently on a non-immigran Bt visa for 12 months and a work permit for the same duration. I don't need to do a visa run every 3 months - I only need to do the 90 day reporting at the local immigration office.

I'm now in the process of setting up my own company. I will therefore need to apply for a new Work permit (which will be under the new company name). The new company will have 2 million baht capital but only 1 other Thai staff.

I'm rather confused on what determines whether I will need to apply for a new non-immigrant B visa and if so will I now have to do visa runs every 3 months? does it have anythng to do with the number of Thai staff/paid up capital of company? i.e. is that what determines whether one needs to do a visa run every 3 months or not?

Any advice would be greatly appreciated

You most likely will not qualify for a 1 year extenson of stay (its not a visa) like you have now. You will have to get a multiple entry visa. See the 2.1 of the police order and its guidlines for the requirements to get an extension.

police_order_2008.pdf

guide_lines.pdf

To be eligible for a 1 year extension of stay based on working, issued by immigration, you'll need a couple years worth of audited accounts for your company. That means that you are stuck with 90 day border runs for that time period.