I can tell you there is an excellent and regular bus service from Malia to Heraklion. It also operates the other way to Ag Nik to. It is reasonably priced, comfortable and runs till late the in the evening.
You will find excellent excursions to various places. Knossos Palace is an example. You can visit the island of Spinalonga. I am sure your rep will contact you with prices etc. But before you book take a walk along the main street you will find several places selling trips that could be cheaper.
Using the bus to Hersonissos you could arrange your own trip to Star Beach. The bus virtually stops outside. There are water slids, ski-ing, paragliding and off course the banana boat.
There are many other trips, Samara Gorge is worth a visit but it does involve a lot of walking. If you do this make sure you have goods shoes, a hat and water.
Hopefully this is of help to you.
Sokin will probably give you further information when he logs in too