If I get this kit, how would I go about dealing with the ecu?

What engine are you starting with? Why do you think you would have to do anything to the ECU?

I have an ej25. My friend told me he thought I might have to do something to the ecu?

MAF will read more airflow, PCM will inject more fuel. It will be fine.

just out of curiosity, where are you getting this kit, what does it come with, and how much does it cost?

any decent machine shop can offset grind your crank but the custom rods will be a pain unless there is another application that has a smaller rod journal than the ej25 crank and the proper length and pin diameter. I bet there is something close out there somewhere just takes a lot of searching.

any decent machine shop can offset grind your crank but the custom rods will be a pain unless there is another application that has a smaller rod journal than the ej25 crank and the proper length and pin diameter. I bet there is something close out there somewhere just takes a lot of searching.

I seriously doubt that there is a suitable connecting rod in another application. The Subarus are already a pretty short stroke/compact engine, and you are now talking about an even shorter rod.