Who did you go to for the advice for water/meth injectors?
The only reason for having water/meth injectors is to lower the temps on the engine/intake paths so you can crank up the boost, and have slightly more advanced timing plots.
The power boost is negligable on them from what I've read, and it will not give you a better set up than a FMIC would. However, getting them both working in parallel would yield some benefits.
What you need to remember is that a CI engine is a heat engine, not like petrol where really cold air = good.
Basically, unless you are going to track the car, or pull big loads up steep inclines then water/meth injectors are a little overkill.
FMIC it first, and you will not have the issues of worrying about constant maintenance and whether your turbo is about to go pop, or whether the manifold is about to make it's own warped shape up.