This all depends on your income targets.

Tip: If you're looking for highest rates, you'll avoid new grads like the plague. They have no experience, so you're talking about competing on price.

For example, I work as a Fractional CTO... charging... well... a massively high hourly rate + percentage of profits.

Agencies who pitch my services have very little competition + the rates they're targeting are stratospheric, compared with new grad rates.

Tip: Start with your income requirements + amount of work you can tolerate. Also client quality you'll be working with + applicant quality you'll be working with.

All these factors set your marketing.

Tip: All the marketing you've listed above leaves you competing with every other similar company on price, so you'll work as hard as everyone else, have very little repeat business, with lowest possible profits/engagement.

Look for marketing venues with zero competition.

For example, speaking at https://Meetup.com groups or other events related to your niche.

When you are getting started there really isn't a way to avoid cold calling. Its a skill and it gets easier the more you do it. The agency I worked at used to do cold call afternoons - everyone did it at the same time, and there were prizes and incentives. It made it fun.

My top tips:
- Get a headset if you can and stand up - gives you more energy
- Take the mindset that you have something amazing to offer and why wouldn't they want to talk to you?
- Make a note of everything so you develop a database of contacts.

One 'blackhat' method of getting leads is to call for a reference for a candidate you are working with. You are much more likely to get through. And you have a really simple opportunity to ask "so how are you getting on replacing this person"

Beyond cold calls, I'd write to everyone (no, a letter, not an email) and include your card or perhaps a calendar or a pen. Introduce your new agency and why you are so good in your niche. Recruitment is one of those things that people don't need until they do - and having your details close at had is a winner.

I'm available for a call if you want to talk more specifics

The best way to startup will be to focus on networking effectively with the stakeholders/decision makers in the niche market. Build a relationship with them and demonstrate you are able to offer quality service.
Second is to do a survey on other recruiting firms offering similar services, gain clarity on their recruitment fees/rates and offer something lower than the market to gain a competitive edge.
Also ensure to have reviews of past client engagements posted on your website/social media handles that your niche market can see in order to establish reputation and trust.