I am delighted you and your friends are planning to come and walk the Causeway Coast.
Other folk have already done an excellent job in introducing you to the delights of this area, giving you good advice on what to see and connecting you via links to relevant literature.
Perhaps I might add a possible plan.
Days 1-2: Base 1: Derry/Londonderry. Explore the delights of the Walled City.
Days 3-5: Base 2: Portstewart. Make several walks from here.You can use local bus services to your advantage, for example taking you on the outward journey or the return leg. From Portstewart west you want bus number 134, and east bus number 140.
· Downhill Demesne, Mussenden Temple and Downhill Beach
· Binevenagh - Area of Outstanding Natural Beauty
· Portstewart Strand, explore the town, walk to and around Portrush
Days 6-8: Base 3: Bushmills. You can make use of bus number 172/402.
· Dunluce Castle and the White Rocks Beach
· The Giant’s Causeway and the coastline as far as Dunseverick Castle
· White Park Bay, Ballintoy, Carrick-a-rede Rope Bridge
Days 9-11: Base 4: Ballycastle.
· Rathlin Island
· Fairhead, Murlough Bay
· Glenariff Glen Forest Park
Days 12-13: You may want to spend single nights in a couple of bases. During the day you might walk in the area of Glenarm and, depending on the time of year, you might manage to explore the Gobbins on Islandmagee. Carrickfergus Castle is on the route to Belfast.
Days 14-15: Final base: Belfast. Explore the city, especially the Titanic Quarter.
The route is summarised as follows: http://www.visitcausewaycoastandglens.com/Portals/0/downloads/CCRMap-French.pdf I hope this might help your planning. If we can be of further assistance, for example with accommodation, please do not hesitate to contact us at Coleraine Visitor Information Centre.