AoA brother.
I tried the Karamber Trek in 2005 from Yarkhun Valley side. We reached very near to Karamber, but i got injured and had to return back from Kishmanja.
There are actually at least 3 different routes to trek till the mesmerizing Karamber Lake.
Route 1: From Yarkhun Side: Yarkhun Valley start from Mastuj Town. From there, a jeepable trek takes u till Lasht. In October / November (when water in river is very less), Jeep can go till Kankhun. From Lasht or Kankhun, one have to trek via Kishmanja, Broghil, Chikar, Lashkargaz etc till Karamber. It is at least 2 days trek till karamber.
Route 2: From Ishkoman Side: I haven't tried this route. Mustansar Hussain Tarar used this route, travelogue of which he has written in his book Yak Saraye. One can reach Ishkoman valley from Gilgit. Road / Jeep trek goes ahead of Chatorkhand... i think even ahead of Imit. From there one has to trek via Worghut, Swinj etc. It is 2 to 3 days trek till karamber.
Route 3: From Yasin Valley (via Darkut Pass): Well, this is the most strenous of the routes. One has to climb and cross the 4200m Darkut Pass. After crossing the Pass, one reaches Chikar and can trek to karamber via Lashkargaz. It is also 2 to 3 days trek till Karamber.
My Advice: One must plan a round trip. From Mastuj to Ishkoman or from Ishkoman to Mastuj. Keeping a full day stay Karamber Lake, it would be a 5 to 6 day trek between 2 last jeepable points.