I would consider car hire.
Gocek the buses stop on the main road and it is a fair hike to the harbour.
I think there is a sunday boat trip which would be another way to vsit Gocek with Carole and Tayfun
By car Dalyan is 45mins using the Gocek tunnel with a 3 lira toll.
The dolmus takes about 2.5hrs
first get one to Ortaca and from there switch to the Dalyan dolmus.
It is a fraction more expensive but getting the large coaches to ortaca which are heading for Marmaris Bodrum etc is more comfortable and a little quicker. These all go through Gunlukbasi.
If you had a car you could easily stop at Gocek on the way to Dalyan.
Yes Dalyan is on the river which meanders from Lake Koycgeiz to the sea and a long sandy beach, through reed beds with rock tombs carved into the mountains on the opposite bank and behind which lie the ruins of ancient Caunos. There is a regular public boat dolmus to and from the beach at the quayside in the village centre. Alternatively there are regular bus dolmus to the other quieter end of the beach where the Turtle rescue centre is situated behind the car park.
Both routes are very scenic. There are also mud baths and hot springs on the river.
Sarigerme is probably easiest to switch buses at dalaman.