ooh i did similar subjects:
in year 12 i did maths (AS and A2), further maths (AS), physics (AS), history (AS). so my workload was more than 5AS's, i also had to self teach the A2 part of maths.
it depends what u wunna do at uni, if its maths/sciency i'd defo pick chemistry above economics, i seriously regret not picking chemistry instead of history.
i'd recommend doing 4, doing just spreads you out too much and you'll get a bad grade somewhere you shouldn't have or ur average UMS would be lower than if u had 4.