Romance consultant as Small Business?

You should be able to do the tasks on a home or separated Small Business as long as you have the required items on the lot. They are normally either socials, or media related (computer, books, TV and music). In regards to using the service as a visitor, I'm not sure what interactions are on a Romance Consultant, if any.

You could set up the lot as an office, but with the way the filters work you might be better off combining it with something busier as you can't use an appointment system, people just come and go at will. You could have an office on the lot for when playing as the owner, but make it into some kind of dating spot too for visitors. Attract Sims (all Sims or choose either Single or Married depending on Career Branch) to the lot, and have your Romance Consultant Get to Know them (buy the Observant Reward Trait or use a similar Occult Ability to help with this), you might want to make notes about Traits, Preferences, Careers, Skills and Appearance when playing as the Romance Consultant, especially when playing as a Matchmaker, so you know who to match with who.

For the lot use the Romantic Aura lot trait, maybe add Convivial or one of the Ley Line traits for Sims who Woohoo and have the Party Games box, costume chest and maybe a couple of WooHoo spots. Maybe sell romantic gift items like flowers, jewellery, chocolates, candies or Flirty consumables like Flirty Heart Cookies, Rose Petal Ice Cream, Cupid's Juice cocktails or Strawberry Nectar. If Sims are on the lot and Flirty it will increase the chance of them interacting with Attractive Sims.