Oh, DEFINITELY ask Clarity for help on how they target their customers and make their money.
C'mon man, would you give that information away? It's called Intellectual Property and Competitive Advantage.
What you should be concentrating on, if you're interested in having a similar business, is the Barrier To Entry.
Your scope is far too wide right now. "Online advice"? Niche it down. You can always expand later, but for now a generalist approach is not going to attract a target market.
The tech, you'll find, is the easy part.
Attracting experts and inquiries...that's another story.
There's the barrier to entry into this market. A minor part of it is putting up the tech...the major part is attracting experts and drawing traffic from those wanting to ask questions of said experts.
You will need systems in place for both objectives. And numbers to support them. How many experts do you need on your platform? And how many people booking calls to them to support your revenue target? And how many people visiting the site to book one call? Lots of freebie seekers out there. Last two inquiries I've had have run once they saw my (publicly displayed) fee. Kind of funny and fortunately not relevant to me as I have real businesses.
Or maybe this is a homework question for you? In that case, you again should niche down, and look for data on those niches. It'll be much easier to find. Maybe target the three or four most popular niches of questions people ask about and add them up. 80/20 Rule, y'know.
The market for online advice is large and growing, and there are certainly opportunities to take your share of that.
So I prefer to give an encouraging answer, and would recommend developing a new platform for a niche knowledge area, a specific language or geography, or a specific profession.
And when you are successful and you have secured a certain market share within the market you have defined, one of the large players may decide to acquire your business!
Back to your question. How to size such market? Well, different professions are at different levels of the digitization game. While business consultants who target startups may operate in a highly digital and online business landscape that includes Clarity, others (such as let's say lighting designers) still have a lot of papers on their desk and visit clients in person - and they see it as the only way to be successful. What I am saying is if you could decide whether you want to be the follower who does things more efficiently or the pioneer in a new market will also help you to decide where you will operate.
Let's take a look at a fictitious example. You want to serve people seeking architectural advice so you recruit experts who are building architects, and in order to make sure they are qualified you require AIA membership (AIA is the professional architecture association). There are more than 90,000 licensed members of the AIA and I can tell you for sure nearly none of them gives online advice. So if you develop a platform aimed at the specific needs of that market (the ability to share drawings online comes to mind) and 10% of the membership would join each selling 3 hours on average per week, then you are talking about a market volume of almost 1,5 million hours per year. I guess they sell at $100 per hour and you take 20% so your share in the turnover - in this example - would be $30MM. You can put different numbers in the equation to calculate the volume based on different pricing or engagement percentages.
Sounds unlikely? Not if you prepare yourself well, find a market with a real need, communicate and deliver a clear customer benefit and offer good support. And - of course - you've got to create a service that really adds to the current relationship between the two parties you match. Would you reach these numbers the first year? Of course not, but how quickly you do reach them depends on your character as an entrepreneur, your desire and ability to work hard and be disciplined, the need for your service in the market you target, and your social skills and ability to secure funding.
If this got you interested, let's schedule a call at any time convenient for you. A 15-minute conversation will surely create a lot of insight!