Just to clarify the situation, once through the access gate there are no other locked gates and you can drive the 17 miles up the Glen and over the Monar Dam to the Power Station at Gleann Innis an Loichel. It is tarmac road all the way but is becoming a bit pot holed in places now.
OS map of the Glen
The Culligran estate has 4 holiday Chalets and a cottage for rent. I have stayed in the Chalets several times over the last few years. They are fairly basic but are an excellent base if you are walking in the area. [No TV but has limited WiFi that is OK for email] They also give you a key to the gate so you can come and go as you please.
The usual start / finish points are not way marked but are fairly obvious if you can read a map or have a GPS.
Hope this helps