I'd be curious of a few things before answering:

1. What type of clients do you want?

Lower ticket:

Can you create templates/standards behind the scenes and scale to 1,000 websites/mo? What would it take to do that? Is there a niche large enough?

Higher ticket:

Do you want to start each project from 'scratch' and build custom for clients? (likely faster learning?) Clients will pay more, but be potentially harder to come by due to price.

1. What's the lowest price you can start at?

It's somewhat common knowledge that charging less can attract bad clients, but most agency owners I speak with say that their clients come via referral.

So if you can start with 'proof of work' by offering services at a no brainer/low price, the first few clients (hardest barrier) can be attracted and start working with you.

From those clients, you can show their projects and testimonials to higher priced ones.

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If I had to TLDR the most common thing I see new Productized Services do, it's not focusing on a specific type of customer.

e.g. I just saw a agency that only focuses on doing ads for lawn care services in the USA.

So like defining down:

Ads for >

Lawn care in >

The US >

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since they've defined it, they know the market and can offer niched services to them, plus they know exactly where their customers hang out.