The best viewing places (with covered grandstands) are Stowe and Copse. The slower corners (such as Luffield) don't allow you to see F1 cars at their best, because they are slow-speed corners where the cars aren't generating any downforce, so they're just crawling around.
If you're going on race day there won't be much chance to walk around unless you enjoy playing sardines with lots of other fans - even between races you won't see much of the track.
By far the best way to experience Formula 1 at Silverstone is to go on Friday, when you will get two hour and a half sessions of practice, you can go and sit in whichever grandstand you want, and if you go to the Becketts/Maggotts section you're fairly close to the track, and the cars are at high speed. Then watch the race on TV, in the comfort of your own home, with the benefit of commentary.
And don't forget that Silverstone is an airfield, which means that it's very flat, with no hills surrounding it, so you will experience the full effects of any wind and rain. Even if the forecast predicts 30c and blazing sunshine. If you choose a grandstand with a roof, the wind and rain will probably come at you horizontally, from the front.
