Er, you only get Big Sister attacks when you've saved all the Sisters in that area, saving 2/3 wouldn't trigger it.
I've been playing through on Hard, Rivet Gun was fully upgraded immediately thanks to its 1 shot kill potential with headshots and the burning is nice for everything. Defending a little sister by that point i just put down a Mini-Turret or 2 and hung around doing whatever i needed with regular or Anti-Personal ammo. I've always got above $600 available and normally hang around near the $800 cap with pretty full amounts of ammo for all guns and 6/6 Kits/Hypos. I'll sometimes burn through a few kits when defending but with Spider Splicer Organs from when they've attacked its not much of an issue.
On a side note, does anyone enjoy using the Drill Rush? I love it vs Houdini Splicers... they appear, i zap them, i charge towards them and knock them straight down. Never gets old.
I've been playing through on Hard, Rivet Gun was fully upgraded immediately thanks to its 1 shot kill potential with headshots and the burning is nice for everything. Defending a little sister by that point i just put down a Mini-Turret or 2 and hung around doing whatever i needed with regular or Anti-Personal ammo. I've always got above $600 available and normally hang around near the $800 cap with pretty full amounts of ammo for all guns and 6/6 Kits/Hypos. I'll sometimes burn through a few kits when defending but with Spider Splicer Organs from when they've attacked its not much of an issue.
On a side note, does anyone enjoy using the Drill Rush? I love it vs Houdini Splicers... they appear, i zap them, i charge towards them and knock them straight down. Never gets old.