Well, this is not an easy question, because there are many factors to consider. You really have to have a vision of what you want for now. If you want >500hp or a 300hp weekend car? For 300hp, you won't need to swap as many parts.
If you buy this car, you will need to swap the motor, trany, rear, brakes, and possibly the wiring harness, injectors, and mass air.

You will need to replace the rear, as the 7.5 will not last long with any slicks and high rpm launches. You can buy a 8.8 for less than $200, then you need to swap it. A gear is a great first upgrade. (4.30s for auto and 3.73 for manual.) The 4cly springs are fine, as they are softer.

The front brakes on the 4cly are smaller and the spindal are different from the v8. If you want to go fast, better brakes are needed. Again, 300hp and the stock v8 with vented rotors will be fine. More than that, and something aftermarket is needed.

Next decide if you want a carb or Fuel Injection. If you buy the 4cly, a carb will be cheaper, as you only need carb, intake, and fuel pump. If FI, you need the wire harness, computer, injector harness, injectors, fuel rails, fuel pressure regulator, mass air meter, and a good fuel pump. (We will save this debate for another thread.)

Trany, you will upgrade as well. A stock T5 will be good for 300hp, but you will want a TKO for up to 600. After that HP, you will look at something custom. This is also assuming you want to shift over an auto.

The engine is another issue. Heads, cam, intake, can get you too 300hp just fine. If you want more than that, after market block and internals would be needed. Also, new flywheel, balancer, and a ton of other supporting parts.... This really depends on how fast you are supposed to go.

Cliff Notes;
I have done both paths, upgrading a 4cly and starting with a stock v8.
If you are going all out, buy the 4cly, as you will be replacing it all anyways.
If you want to just do pieces here and there, and you get bored quickly, buy a v8 and just upgrade a few items at a time.

Hope that helps out, this really isn't an easy answer.....

 

Thanks man that helped alot.

I think I will hold out for a V8, sounds like it will save some time and money along with fitting more into my plan.

 

Oldman is all over this one....my work here is done!

 

I have learned all that you taught me....

not all that you know....

 

put a 2.3 turbo in it 300 hp is not a problem. it only costs money