I believe it is possible to just get the Business Visa without the work permit (since you probably will not have 4 staff)
BUT be aware your business as a company as opposed to your gf owning it 100% as a sole trader is going to have a shitload more paperwork, headaches and tax. If it is a small business that you are not expecting to personally earn
*****
baht a month then don't form a company. Let the Thai run it as a sole proprietor and find a cheaper visa option
Apart from the wishful thinking of getting a Business Visa (possible but going to incur so much extra costs almost certainly not worth it). The biggest mistake westerners make is thinking they need a company and do it all official. They forget or never know that if the shit hits the fan, they only deposited 10% of the 2 million baht required. The rest is due when the company is closed or legal action is taken. Unless you are paying more than 2 million for the bar. It is not worth it.
So to answer your question, yes you probably will be able to get the Business Visa, but unless your paying close to or more than 500,000 for the bar you are buying. Getting the Business Visa will end up costing your business so much more than what you will save.
For small purchases to keep the gf or wife happy it is better to consider it a gift and salary (and sick buffalo) all in one and up front gesture (as opposed to a monthly allowance). And if things go south to consider it a gift. Probably nothing you do not already know after living here 10 years.