I wanna start watching Doctor Who... but Netflix only has seasons 5-9... is it necessary to know the show from season 1 on to understand it? or are the seasons individually completed?
They're individually completed.
They are some occasional references to previous seasons but nothing too confusing.
Only problem is that S2-5 is David Tennant, who most people feel to be the best Doctor
Try not to think about continuity too hard when watching Doctor Who.
It's not necessary but I would recommend watching from the beginning (of the new series)
just watch one season, they're all pretty much the same.