Each of those questions is a multi-layered answer, and rely heavily on what other modifications, kit brand, etc. I'll try to cover as much as I can, and provide some follow up questions where I need more information to assist:
At what boost does your system begin injecting?
* Depends on the kit, if it's a single stage kit we start spraying at 10 psi, if dual stage we start a partial spray at 7 psi and a full spray at 13 psi.
What size meth nozzle?
* Depends on your power level and the kit. For example, the Snow kit at 450hp and 10-15 psi recommends the #5 nozzle (375 ml/min); the AEM kit with the same specs recommends a 500 ml/min nozzle.
Power increase or E.T difference using meth?
* We've seen a car that runs 12.8s with a tune and cai jump to 12.2s on methanol. It provides around a 40hp bump in power.
Other mods and tuner?
* Completely up to you. We have had great success with our methanol tunes and our customers love our tunes and support in general. Mods can be as mild or as wild as you want, I've seen anywhere from a completely bone stock no tune running meth for lower IATs all the way up to FBO aftermarket turbos running it as a secondary fuel source.
Hope that helps! Let me know if you have any other questions. We are a supplier for most SHO aftermarket parts and also offer our own tuning solution, so let us know if we can help you reach your goals.