I would never use a .co to run a business without having the .com as well. Too many people would by habit use .com when typing your site in their browser. If another company owned the .com, you could very well lose a lot of business.

First thing you should start working on your website.I assume you just customized a billing software.

There is no way a customer can trust you to host his website with you. No TOS / AUP which is very important for any hosting business.

As you know there is a huge competition in this business.To compete with others atleast you should have clean content oriented website which provides information about your products / services.

I would consider buying a .com first, then using ad websites such as cpalead, Adwords, and so on. Market your websites like that. Or start advertising on not so popular websites to keep the prices down.

If you gonna invest on your future first step without any doubt is Local Market , You should try to get many testimonies from your local market which could help you to be a reliable company in other type of markets .