what should I use ready to use software or a custom?

Hi
If you haven't already validated the market, then it would be best to start with something simple and the option with the cheapest costs.
If you see that there is in fact a need for your service, you can always start developing your own version whilst the template version is running.
If you the costs of the templates are close to the costs of the 'made from scratch' (MFC) version (which would sound strange), then you need to take into account the following:
1. MFC version usually takes longer
2. MFC version usually has additional 'surprise' costs.
3. Template version has limited ability to make changes.
If you decide to go for the MFC version, make sure that:
a. you have a development contract with the developers
b. you chose developers that you can trust (have recommendations).
c. Don't ever pay the entire amount upfront. Always pay only after each milestone has been done, and leave at least 25% of the payment for at least 2 months after they have signed over the project (in case you discover bugs).
d. Make sure that after every stage they send you the code.
Good luck
I've successfully helped over 350 entrepreneurs, startups and businesses, and I would be happy to help you. After scheduling a call, please send me some background information so that I can prepare in advance - thus giving you maximum value for your money. Take a look at the great reviews I’ve received: https://clarity.fm/assafben-david

Various software solutions are not a problem but a market
I would love to help you create a market
and find people who will support the product
marketing and distribution are the biggest problem you can buy a domain and launch a product but if you don't have people who will sell something you are in trouble, the idea itself doesn't make money.
If you need help with your project and you don't see the market, feel free to contact me, I've worked with 3 big startups that are quite similar to yours.

Buying a clone of existing website adds nothing to it. If you really want to start something new then make sure it is new. I would go with custom solution from ground up with different features. Otherwise just buying a clone of a website is just going to be a marketing nightmare when it comes to market your product once it's launched.

The first and foremost question is why do you want to start a freelance marketplace?
What need can you solve which Fiverr, Upwork or Guru aren't solving?
What differentiates you from any of those platforms?
Without any of those answers, you could end up wasting your money buying the clone, however little it might be.

If you have a specific niche in mind or a specific requirement you want to fulfil, will the clone do the job to test your hypothesis? The purpose of the clone can be as a basic MVP to test your hypothesis, and once validated and the learnings gained from the test, you can then go the next step, add some customization into your custom product.

You should always try to find software on the market that will suit your need before writing your own.

Ready-made software (open source or commercial) has quite a few pros included:

Updates
Support
Maintenance

Writing your own software is a long term commitment and if you are not in the software business or you are not planning to be in the software business in most cases you would not be able to deliver and maintain good quality software.

That said there are lots of cases that you will need some sort of integration or customization that would not be achievable by using a proprietary solution.

There are many fiverr clones and Wordpress themes available online, you shall evaluate all before making a purchase.

I've successfully helped over 150 entrepreneurs, startups, and businesses, and I would be happy to help you. Please send me more information before scheduling a call - so I can give you maximum value for your money. Take a look at the great reviews I’ve received: https://clarity.fm/ripul.chhabra

I would not go with a "clone in a box" solution, but I definitely would use ready-to-use services that are out there to build what you need while allowing some level of customization.

For example, you can use tools like Wordpress (CMS), or Shopify (e-commerce), or other similar tools to build your marketplace, depending on your needs. This will allow you to get your idea up-and-running quickly with little upfront investment.

After you've proven that your business idea works, then - and only then - you can go back and invest in creating a more custom solution.

Buying a clone script is not the right choice to create a website or marketplace for your dream business. As you mentioned, two approaches that can be chosen for building your freelance marketplace like Fiverr. I would suggest you choose a full-fledged freelance marketplace software.  Considering a ready-made solution can be a more advantageous approach compared to building a website from scratch. 
Here’s why:

Benefits of Using Ready-Made Software:

Cost-Effectiveness:- Developing a marketplace from scratch requires significant investment in terms of time, money, and resources. Ready-made solutions, like the Fiverr clone, provide a more budget-friendly option as they come with pre-built functionalities.

Time Efficiency: Building a platform from scratch can take months or even years. Ready-made software can significantly reduce the development time, allowing you to launch your marketplace much faster.

Proven Functionality: Ready-made solutions are often tested and refined over time. They come with essential features like user profiles, job postings, payment gateways, and reviews, which are critical for a freelance marketplace.
Technical Support and Updates: Providers of ready-made software often offer technical support and regular updates, ensuring your platform remains secure and up-to-date with the latest features.

Scalability and Flexibility: Many ready-made solutions are designed to be scalable, allowing you to start small and expand as your user base grows. They also offer customization options to tailor the platform to your specific needs. YoGigs is one of them that caters the demand of freelance businesses.

Clone vs. Full-Fledged Marketplace Software

While a Fiverr clone can offer a quick start, there are full-fledged freelance marketplace software solutions that may provide a more comprehensive and flexible approach.

Here’s a comparison:
Clone Software:
Simplicity: Clones are designed to replicate a specific platform, making them straightforward to implement.
Basic Features: They typically include only the core functionalities found in the original platform, which might limit customization.
Short-Term Solution: Ideal for those looking to launch quickly with basic features but may require significant modifications as the business grows.

Full-Fledged Marketplace Software:
Robust Features: These solutions are built to support a wide range of functionalities, including advanced search filters, detailed analytics, and diverse payment options.
Customization: They offer greater flexibility for customization, enabling you to create a unique marketplace that stands out from competitors.
Long-Term Viability: Designed to support long-term growth, these platforms can adapt to evolving business needs without extensive rework.
Best Software to Develop Freelance Marketplace like Fiverr

YoGigs is a viable option for startups and aspiring entrepreneurs searching for full-fledged marketplace software solutions. It offers advanced features tailored for freelance marketplaces such as user management, service listings, secure payment gateways, powerful admin tools, and many more.

YoGigs is a cost-effective and fully customizable solution so businesses can customize it as per their needs or requirements and you can launch the Fiverr-type website within a short period similar to a clone.
Unlike clone scripts, with YoGigs you will get a professional-looking website that attracts users and provides the features that need.

You can explore more: https://www.yo-gigs.com/