I havn't done it, but I imagine rally is a huge logistical nightmare. You need more than just a job. You also need to know people already in rally, plus you need a father or uncle that is the practical sort, and he needs to have a 4WD and a car trailer. Plus your best mate needs to be an A1 mechanic. Plus your girlfriend navigator also needs a job (huge fuel and entry fees, plus helmets etc), plus she also has to run the whole business side of the car like getting sponcers etc.
Or you can be a celebrity or company dirrector, and buy the friends/mechanics you need.
If you are heading to do real rally oneday, then get out the CAMS rule book and look at engine swaps and stuff your allowed in your class. Then look at all the CAMS safety gear you need.
I think you will have to run a non-turbo motor, and a motor originaly offered in the shell your using. Which would mean no KE70-4AG. But yes to KE70-2TGE. And yes to AE71 with weber carby on 4A-C. Or KE70 with sidedrafts on a 4K.
But if you just doing motorkhanas and stuff, build any car you like. But do yourself a favor as a driver. It's not just about the car, it's about you as a driver. If your project in beyond you, you will never get any driving practice and your yooth will be wasted. Build a simple car (eg stock KE70 with a Weber and zorst) and spend your money on events and tyres. You will become an ace driver!