Hey @Jonathan_SAYEB, welcome to the Community!
You realize the answers you’ll get on such questions would be experts for hire (myself included ngl) giving advice that puts themselves and their agencies in the best light? 
Let me try answer this so that it’s fair in general. There is a pool of Coda experts and agencies here — this could be a good starting point. Most of us are on that list, but also there’s a couple others who are not. So you could also make a request topic in this category and have people answer to that.
The pool, of course, is not as vast as the one of Excel or Notion experts yet, but there is already a selection of experts of various backgrounds, skills, pricing levels, geographies, and ways of work. Agencies tend to have stricter systems (bureaucratic sometimes) while small teams or individuals would keep things simpler and human, at the expense of maybe not being as predictable as agencies are (think factory vs craft manufacturing.) There are also consultants whose specialty isn’t Coda itself but who are experts in their own domains (Financing, Legal, AI etc) and just use Coda as a tool of choice — their solutions might not be as sophisticated technically but if their domain-specific skills are what you seek, you could have a much better synergy with them and get much better results.
On the skill part, if you need simpler, “Gallery-templates-level” docs and maintenance then anyone would do. But the further you want to push Coda in terms of solution size, bespokeness, complexity, and sustainable performance, the more it will matter that the expert you choose has deep skills.
On the approach part, you have to figure where you are on the spectrum between “I just need working hands to implement my requirements” to “I’m looking for a partner with whom we’ll be solving this”. If you’re on the former end then probably choose an agency, and if on the latter, look for individual experts and pick whoever feels a good fit by personality and also skill. As a general tendency, agencies would require more defined and formal requirements whereas smaller teams and indies could work with more blurry ones and help you shape the vision, chiming in on what’s sensible and possible to do.
Being honest with everything about the project, the budget, and any sorts of limitations is always welcome, too. Also the more you can tell about the project in advance, the faster you can find a hire who’d be interested in such kind of project (e.g. I personally hate working on trivial stuff and only find joy in applying myself at building something truly creative, but I have a partner to offload the boring stuff to.) On the budget part, this is normally discussed individually. The mean rates for such work is in the vicinity of $120/hr-$350/hr. And of course there are people working at near-$1000/hr rates as well as people working at $50/hr, and agencies only reselling and retrofitting existing solutions, and agencies only taking in projects that are in five digits and above. Not sure if this is more helpful or confusing though — just leaving this here to set expectations about the current state of Coda consulting market.