If you go to Omalos with your own car in order to walk through the gorge of Samaria you will be forced to get back to Omalos to retrieve your car and it is not always such a good solution.
Alternatively there are public buses (KTEL) going to Omalos from Chania every morning (only when the gorge is open). Once you have walked through the gorge and are in Agia Roumeli you take a ferry boat returning to Hora Sfakion (or Sougia and Paleochora if you prefer but there may not be a connecting bus to Chania) and take an evening KTEL bus back to Chania.
If you are not alone, why not share a taxi to Omalos? The cost from Chania to the entrance of the gorge is Euro 70 (2014 prices) for up to 4 persons.
The most common way to "do" the gorge is to book an organized tour. This can be done from most places on the north coast (some come from as far as Agios Nikolaos or Ierapetra, which I wouldn't recommend because it entails an almost 24 hour round trip!). You will be picked up from and returned to your hotel. The buses are air-conditioned and you have the benefit of a guide. This does not mean that you need to walk in a group: everyone walks at their own pace and meets at a prearranged time and place in Agia Roumeli. These tours are not very expensive and can be booked locally, often directly at the hotel where you are staying.
If you must, it is also possible to drive to Omalos with your own car, park it there , walk through the gorge, take the ferry back to Sougia and then take a taxi back to your car from Sougia (about 40 minutes drive). But you must pre-book a taxi as there are only two taxis that operate from Sougia.
Stones , stones and more stones! The terrain is stony most of the time but it varies. At the beginning the path is paved with uneven stones, then at times it is more like a forest path with some earth. Once you reach the river bed you walk mainly on pebbles (which is tiring on the sole of the feet). You also have to cross the river at least a dozen times, sometimes on small wooden bridges but more often by stepping on rocks. These have been placed at strategic intervals but still require some sure-footedness. The only easy path is once you leave the southern end of the National Park: it is flat and there are no stones, no shade either so that the last 3 km can be really really hot in summer.
A walk of 16 km on flat ground should take just over 3 hours if you walk at a brisk pace. This is theoretically quite easy in the gorge of Samaria as you are going down most of the time but the path requires some care and attention and the walk will take you a minimum of 4 hours of walking time. Add to this time to rest, to stop and look at the scenery, take photographs and you can count about 6 or 7 hours to cover the entire distance.
The walk is long and can be arduous but it is not a difficult walk. Still, every day people get into trouble or end up having an experience which is far from pleasant. The most common factors are:
Most young children have no problems walking but will not hold the distance. You might end up having to carry them which is nobody's idea of fun on such a long walk. It is better not to take children younger than 8 or 9 unless they are used to hiking. From that age onwards they generally have far less problems than their parents but they tend to walk a little too quickly, jump about ...and fall. Make sure you have them in sight most of the time (or at least ensure that you know if they are in front of you or behind!) and try to get them to slow down when they get carried away.
You may take your dog with you in the gorge provided it is on a leash at all times.