I would strongly recommend you include Lake George in your itinerary. I have been to the area many times but I never tire of it because it is so beautiful. I used to stay in Saranac Lake to save money but most of the lodgings there are no longer a bargain. You can stay right in Lake Placid for a reasonable price if you go during week days. There are even deals to be had during weekends there if you choose the right place. The Northwoods is in the centre of town and only charges $79.00 during week days. There are a couple of highly rated motels a ten minute walk from downtown that can be had for around $100 even during the weekend. A couple that come to mind are The Northway Motel and the Alpine Motel. Last year I stayed at the four star Crowne Plaza during the week for $ 140 a night.
I've never taken the ferry across the St. Lawerence so I can't comment but I alway exit 401 at Ivy Lea bridge to USA, and proceed south on I-81 to #3. There are many way to get to #3. You can even by-pass Watertown easily. I planned a trip to the area for some friends from work who had never been to the area. They just returned and thanked me profusely for directing them to an area that just blew them away. They left last Friday and spent the first night in Watertown. From there they proceeded on #3 and #86 to Lake placid where they stayed for the night. The next morning they took 86 to the top of Whiteface Mountain. Then they followed 86 to 9N and headed for the Chimney Point ferry crossing into Vermont. In Vermont, I had them head north east on 17 through the appalachian gap and Camel's Hump mountain until #100 where they headed south until they reached 125. From there they proceed west of 125 which looped them back to the chimney point crossing of Lake Champlain. They then proceed south on 9N until they got to Lake George. From there they took 9 back to Lake Placid. My friend's comments about the ride were like this. They loved the Vermont portion , 9N, and Lake George blew them away. The mountains around Lake Placid are stunning, but the town underwelmed them. I'd have to agree with their observations.