Usually they mean slides, but in this case they're probably strums, but listen to the song for the correct strumming pattern, etc...
so does it some times amtter...cuz at one time theres 2 slashes and at others there 4
In my opinion not really, it doesn't matter, as long as you know the chords, just match it up with the way the song is played, or make it your own.
Don't worry too much about the I's, it probably means to go to the next chord. Reading tabs is a voodoo science sometimes, the main thing is that you have the chords to play with.