I don't have answers to your direct question. I only have 2 week's experience traveling in Greece/Crete, but I'll reply based on my experience and perhaps others will chime in. On short-trip car/passenger traditional ferries we were always asked (firmly) to leave our luggage to one side on the car deck, which is the deck that you initially enter when walking onto the ferry on foot. So we didn't have to take the luggage up stairs or very far onto the ferry. Since the same ramps were used by cars to get on/off the ferry, we were able to roll the luggage and not lift it. It seems there are no security concerns with theft as everyone seems to do it, and once underway that area is roped off to passengers. I would pack as I do for an airplane trip so that anything valuable or essential is in a smaller bag that can stay with me.
On the largish overnight ferry that we took from Chania-area to Pireaus, we booked a cabin. We did have to take the luggage up 2-3 levels from the car deck, on set of escalators. That took us to the check-in desk for the cabins. At that point there was a line of porters waiting to show us to our room and handle the luggage. If we hadn't booked a cabin I think we would have followed the same pattern as the previous paragraph. The next morning, leaving the overnight ferry, I don't remember seeing porters but it seems that it would be possible for you to arrange that through the 'front desk' on the ferry.
The cabs were able to get quite close to the ferries so we didn't have to go far with the luggage. At Pireus we used Welcome Pickups https://www.welcomepickups.com; the driver was waiting with sign with our name on it, just like an airport pickup. He immediately took most of the luggage and we walked the short distance to the car. We also used Welcome Pickups to go from Athens city center to the airport, to avoid the hassle of bus or metro with our luggage. They'll provide a quote on their website. I'm thinking it was 38E for two from an Acroplis-area hotel to the airport on a light traffic Saturday morning. You might want to ask the Welcome Pickups staff if they know of a porter/assistance service. They offer more than just transportation, so perhaps they would be able to help. It doesn't hurt to ask and perhaps they have a referral.
In one case it wasn't possible to be dropped off directly in front of the hotel, but about a block away because we were in a historic area. The hotel owner walked out to meet us at the cab without our even asking and helped with the luggage, and then walked with us back the same way after we checked out all the way to the cab they had called(!) I can't say you will get this kind of service everywhere but people are generally very hospitable and eager to help. We found almost all cabbies very helpful and interested in lifting the luggage into the car trunk. Cabs are inexpensive.
