The Greddy ProfecB SpecII will act as a boost gauge too so you might not need a gauge. I don't have an actual boost gauge, just use my Profec.

What brand injectors? I would recommend 550s.

If you go with Hondata, you do not need an Air/Fuel gauge. Plus, a simple LED Air/Fuel gauge is very deceiving and not very helpful. You might consider an oil pressure gauge and an EGT gauge.

You will likely spend a bit more on fittings than $50. You need to take into account that you're going to need to place a pretty large fitting setup on your oil pan for oil return on the turbo. The return line should also be well insulated because it will likely run very near the downpipe.

How much do you want to get out of this setup? How much boost? What are your future goals for it?

Also, you really are wasting your money on that piping kit because it's a do-it-yourself kit which means they provide you with a few bends and you need to fit it and weld it up. Just get a few bends from JCWhitney or something and have a shop weld it all up for you. That's another fee you will run into is that of a welder regardless if you get the DRAG piping or not.

Finally, budget between $300 and $500 for tuning after you have the Hondata installed. The basemap is just there to get you around town and to a tuner. After that, you're at the mercy of the dyno and tuner charges.

Hope that gives you some more info.