Hi Louise, give www.viamare.com
a ring/email. They are London based and excellent.
They are always our first place to get a quote from. Last time they were cheaper than booking directly with the shipping line and also offered us more flexibility. (We book an 'open' ticket for our return as we never know when we will need to be back in the U.K....our primary base). One of the ferry companies (can't remember which one), would not allow us to do this last April. - Not a problem if you intend to stay on Kriti permanently, but for people like us who share our time between the U.K. and Kriti it is useful.
We have recommended them to friends who have a house on Andros and spend 6 months of the year there. They also found them the cheapest and easiest company to deal with......and have shared the information with other friends who also travel to Andros regularly. - At this rate I should get commission! Seriously though, they are worth a ring.
All the information you have been given is good advice. Warwick's comment about arriving early is useful. We were prevented boarding until 7.00pm in Piraeus on the Blue Star line on one occasion, but ANEK always seems happy to let you board early.
Re Ancona, the ferry crossings from there get very busy, but at Bari you can almost turn up and take a chance of getting on the next ship if you are not travelling at a busy time. As you want to sail from Bari it might be worth thinking about if you are not in a rush. Discounts can then be available....but not guaranteed. We always book ahead as we are travelling with animals, but we have seen others getting a good price reduction.