You will need to ask your accountant or financial person the best way to organize that, but in terms of marketing, you have two choices: to use it as an "added-value" service to your existing service, or market it as a separate service under a different name, logo and trademark.

My first question would be is there a market for this business? Is it something that your customers typically buy with your current products or services or is it something they are asking if you offer?

Starting out, I would say to "test and measure" the idea with your current customer base to make sure it is a service or a product they really want to buy.

Then, add it as an additional service or as part of a "package" of services you offer and this package may be at a price point slightly higher than you are currently charging.

Test first before committing resources and marketing dollars and efforts to generating more leads to a new business.

You have the advantage right now (at least it sounds like it) of a "captured" base of current customers. Go back to them first. You already have a relationship with them and a reputation for your work.

Grow your "start-up" from this base, and you'll have a better idea of your new idea is a winner, and deserving of its own unique company.