nacho – Yes, you canm come down early or stay later. Friday and Saturday nights are covered in the ticket price. The extra nights are booked direct with Avon Tyrrell. I know a few families who are doing similar.
There are various trails around the New Forest with varying degrees of legality. There is little to really challenge in terms of big descents or climbs but it is pretty and there are wild horses, cows and pigs wandering free.
It is actually a good place fora holiday in the NF as it is nice and central but close enough to Bournmouth for sand castles and ice creams on the beach or the rest of the coast for nicer, quieter beaches.