1. As long as you aren't driving on I-66 towards D.C. during morning rush hour (6:30 am to 9am) or away from D.C. during afternoon rush hour (4 - 6:30 pm), you shouldn't encounter any horrible traffic from Standardsville to Arlington National Cemetery. There is always the possibility of a accident or even unexplained slowdowns, but I wouldn't be too concerned about traffic outside of the above-mentioned times. Just use GPS or Google Maps (whose directions look just fine to me) to get you to the cemetery. Fortunately, you don't have to drive in D.C. to get to the cemetery, so that's one less thing to worry about.
2. There are two ways to tour the cemetery--on foot or by taking the Tourmobile hop on/hop off bus. The bus originates at the Visitor's Center and makes stops at the Kennedy Gravesites, Arlington House (the Lee mansion) and at the Tomb of the Unknown Soldier. The tour goes around other places in the cemetery and you will be shown the graves of prominent people (but no stops). There is also live commentary on the bus. However, you can do the same on your own just by getting a free map at the Visitor's Center (or online) and walking. Do be aware, however, that the cemetery is hilly and it's a fair hike from the Visitor's Center to the Tomb of the Unknown Soldier. I would allow a minimum of 2.5 hours to tour the cemetery and Arlington House and more if you'd like to explore some other areas such as Section 60 where many of the casualties from Iraq and Afghanistan are buried or the graves of prominent people.
3. As Carol mentions, there's a lot of threads on the Washington D.C. forum about how to get to the Lincoln Memorial from Arlington Cemetery and I'd look there for more information. Basically, you would be on sidewalks the entire way, even walking over Memorial Bridge, but there are a couple of roads to cross so be careful there. As long as you have no mobility problems, it should not be difficult to walk. Once you get to the Lincoln Memorial, you'll be on the National Mall and you can easily walk all the way to the Capitol if you want. The nearby monuments would be the Vietnam Veterans' Memorial, the Korean War Memorial and World War II Memorial.
Some links which may be helpful: