We used the Ancona route as we like the Anek ferries. Ancona was very easy to negotiate but the queue to actually board the ferry got a bit chaotic. Mind you we were late arriving and were virtually right at the back and got tangled up with the boarding line for Igoumenitsa and couldn't get out of it. No problem though as the loading officer just shrugged and directed us off to one side of the deck space reserved for Igoumenitsa. As it turned out that meant we were nearly first off at Patra. The nineteen hour voyage was very relaxing after the drive, too. One of the good things about Anek (certainly if coming to Souda) is that you can get on the boat virtually anytime. It leaves Piraeus at about 9:00 p.m. but we were able to board as soon as we arrived at about 4:00.
Patra to Piraeus is very straightforward being excellent standard motorway for most of the way. It is a toll road but when we did it four years ago the total cost was about €4. From the motorway to the port was easy enough, too, with decent signage.
Personally, I wouldn't bother with satnav. I did our planning using the viamichelin site (which was excellent then as has been improved since). You can check shortest route, quickest, michelin recommended, M-way or avoiding tolls etc., etc. Michelin give well detailed routes with clear instructions and you can, if you wish, break the route down into very short sections to get good detail to go through or round towns.
Through France we avoided the M-ways and used the A roads instead. For quite long distances they're quite close to M-ways so if you get delayed you can divert quite easily. Our experience of the French non-M-ways was that they were fast, safe and didn't carry much traffic. We didn't use the Italian autostrada on our return journey either and that was straightforward, too.
With the ferry companies, whichever you use, book the international and domestic parts of the journey at the same time as most (if not all) the companies give a decent discount - and another if you're going back and book everything together. (We did Crete/UK/Crete).
The best maps I found for France and Italy were the Hallwag International ones. http://www.hallwag.com
. Very clear and include larger scale insets of many of the larger towns.
P.S. If you want links to ferry company sites they're on my web site if you click the www button below.