few things:
a) you don't need a sump
b) you don't need 1lb/g of live rock
c) a 75g is going to be a bit small for most tangs, they're just too active and a 4' tank isn't very long
now that that's been said:
a) a sump is an incredibly adaptable and usefull filter, there isn't a better one.
b) live rock is an amazing bio-filter as well as being very interesting to watch, you can cut costs back a lot by making your own base rock out of concrete, crushed coral and argonite sand for about $.75/lb and then fill in the gaps with really high quality live rock. about 3/4 base and 1/4 uncured live rock will provide a nice look after a few months when the life has a chance to spread from the live rock to the base rock.