questions about xbox live for the 360

[Erman_94]

i have had the 360 for a long time and now i finally want to experience xbox live. i have the following questions:

1) on the xbox site it says a silver membership is free, so if all i wanted to do was receive updates/add ons for games and not play them online would this be sufficient?

2) if i receive updates online, do i have to have the ethernet cable connected at all times to have those updates visible? (for example if i update songs on guitar hero, would i need that ethernet connected in order to play those songs?) (i dont have wireless internet)

3) also, would it cost many to update these songs? or is that only if they are those 3 packs?

any help would be appreciated, thanks