Cubase 7.5 or AI for home recording with NI vsti's

First a bit of background…Been out of the loop for the last 7 or 8 years and want to get back to recording for fun. I used to run a PC with Sonar 5, FX Pansion Guru, a Delta 8 bus 24/96 and a few outboard rack effects. I lost some steam after the motherboard went on my DAW and more importantly had my daughter.

Few questions…

What kind of computer specs are needed these days to keep up with a host of vsti’s/vst’s? I’ve got a 2 Ghz Mac Air with 8gb of 1600 mhz ddr3 ram. I’d rather not use this small laptop though and would like to keep my DAW dedicated and offline as much as possible. I’d like to build something with a budget of around $300-$500. I do not want to deal with latency issues so please tell me if I need to increase my budget.

Looking for a good affordable soundcard that runs almost latency free running either Cubase 7.5 or AI, Native Instruments vsti’s (Absynth, Electric Piano, and probably a few others), as well as effect plug ins like Waves, Izotope,etc… ?

Most the music I make is in the box with some guitar, bass, and occasional vocal.