Med Help Needed/Do we need a concierge service?

As you don't have a captain at this point so can't possibly address the experience and knowledge the captain has in the med, then we can't answer that.

Well, it depends on the Captain and their knowledge and experience. Let's talk the extremes. If a Captain was Italian and had spent their career cruising those waters, knew people at all the ports, had experience booking at all the marinas, then you wouldn't need a concierge. If the Captain had little or no experience as a Captain in those areas then you definitely would. The closer you come to the first situation the more likely you can get by without a concierge. This is why you have those saying MUST vs. those saying NOT. Something as simple as what languages your captain is fluent in will be a factor.

Not trying to be difficult but the answer is not a clear yes or no. It is dependent on your captain.

When you have a captain hired then discuss it with them based on their past experiences there. If then in doubt, use a concierge to avoid problems. If your captain can't answer those questions, then you've chosen the wrong captain for this adventure.

Greater questions will surround the legal aspects of your cruising rather than reservations. You've indicated 5 months in EU countries, more importantly Schengen countries. Unless rules change between now and then that presents you with Visa problems. You don't indicate whether the boat is tax paid or not. Depending on your specific plans that could become an issue. Your agent you use to handle "import" and entry and other boat and Visa issues may provide all the advice you need in that regard plus assistance with reservations.

Wish you the best of luck in your trip. Once all details are worked out, it should be great.

You sound like a self-sufficient cruiser who doesn't normally use a F/T captain. I'd say you'd do well to use both, although the captain need not be full-time. You'll be dealing with different languages, phone and electrical systems, etc. One source for reservations, knowlege of regulations or locating mechanics, etc. would be a great convenience. A captain with local knowledge and contacts would also be a great convenience, and could keep you out of trouble.

Sorry to disappoint you olderboater, but my yacht is staying for more then 15 month in Greece an EU & shengen country.
A non EU flaged yacht can stay up to 18 month in the EU without any restrictions, after that you have to leave EU waters or freeze the yacht for six month meaning in other words, to deposit her papers with the customs authorities.
That is what I was told by the greek authoriets, and that what I'll have to do in two month.

You don't disappoint me either of the three times you posted. There are two issues, how long the boat can stay and how long the people can stay. On a Schengen Visa that limit is currently 90 days out of 180. It is still possible in at least one country to get a visa to allow longer in that country and not have it count as Schengen. However, most people take the easy way and spend 90 days in Schengen and 90 days out, then 90 back in.

Schengen has nothing to do with the boat. It's about the people.

As to the boat, each country has it's own rules too as to various tax issues. They also have their own VAT rates. Then the history of the boat can sometimes come into play. Far too many complications for me to ever attempt to unwind without a professional.

I assume you have some form of resident visa or other special visa in Greece or may be a citizen, rather than Schengen, if you're staying there 15 months yourself.

Also note that the rules for the boat vary based on where your residency is.

I woukd say that whilst a concierge service never used to exist and the Captain managed to get everything organised himself that given the amount of paperwork and other BS required these days the use of an agent is recommended in most places but especially Italy

In Euro most they are called a "Conciege" in simple terms was "employ an agent" the Concierge no doubt adds a degree of sophistication to the agreement and makes the owner feel really good about paying way too much for simple service..
I was born and raised over there and sure recognize the difference in terminology and of course the corresponding cost.
Just my 2c . no intent to tick anyone off...

I would recommend using agents for specific ports. Most of the ports booking systems are on line in France. If you want to use an agent then it makes life easier. I am based in Mallorca and i usually use an agents in some ports of France like St Tropez or Cannes. For Italy i always use an agent due to the language barrier and trying to get a mooring without one is not always the easiest.

There isn't a clear-cut answer to this question. The agents are a matter of convenience, but you don't require them (except for a few select ports, where they won't speak directly with the captain). That being said, they are often very good at greasing the wheels by overcoming the language barriers and local practices.
Don't shy away from them as a rule, but be careful to choose agents that have transparent billing practices. The difference between an agent and a concierge is that agents work on fees, rather than a salary and gratuity. You can pick and choose when you want to use them, and for what services. When we cruised the entirety of the Med a couple of years ago, I had several agents that I used (and I chose the best agent for my needs each area) and I don't believe I spent more than $5,000-$10,000 in agency fees all summer. That small amount (in comparison to our season's budget) was well worth the convenience.
That being said, finding a resourceful captain is surely important.