APEXi AFC controller is a useful controller in projects like these.
Are you lowering the compression ratio? The current engine will not cope with much extra boost, so the absolute limit is around 10psi and I'd say go lower than this for safety.
As an example a single turbo giving 7psi of boost will push you to around 216hp to 247hp, at 5 psi you get to around 197. A lot depends on the engine condition and how well the exhaust flows.
Due to compounding (compressing already compressed air) a twin charge system is likely overkill when you can get a max power figure with a single turbo. Plus you have to setup the chargers to work together.
That said some people just like a challenge and will happily do off the wall stuff to create something unique.
An electric water pump and better radiator will help keep engine temps down, but you'll be running a lot of heat from the compressor so an intercooler is a must have, and you can add water injection mist to cool this further for track days, but on the street when you'll typically do short bursts of power you don't need to go this far.
If I was twincharging this i'd use a small turbo and supercharger, to minimise lag and give flexiblity. I'd set up the supercharger to come in first, then switch to the turbo as well as the engine rpms increase. Mapping this will be a pig and you need to be spot on with the fuelling and will certainly need a knock sensor.
