Hardware and config advice

I am hoping someone can help. Looking to build an inbound asterisk based ivr with 8 pri circuits; the db from which info will be queries is mysql.
Trying to build a redundant system. I can envision building 2 servers with 8 pri capacity each, but how do I make them either redundant or do load balancing?
To handle 8 pri circuits with approx 180 concurrent calling capacity, what kind of hardware would I need? CPU, ram etc.

Second, if I decide to use SIP trunking instead of pri lines, what kind of hardware is recommended.