I Used to use Magnum a lot for bittering, but nowadays I prefer to just use up the hops that I've bought for late additions.
It does depend how they sell things, over here, 30 gram packs are almost 60% cost of a 100 gram pack, so I don't see the point in buying small packs or having 20 odd packs with a bit of some hop.
As for smash, my favourite recipe is:
5 kg of vienna (viking malt in my area, cheap and good)
100 g of whatever hop you want to try, spread over 60, 20 and 5 minute additions to get about 25 ibu's
1 pack of danstar Nottingham, ferment at 20 degrees Celcius
Tune for your system to make about 22 liters of beer.