Kaido,
your getting sound advise from these guys!
I have some knowledge about this as well as i did build mine to race against some serious factory race cars. And to be perfectly honest we built a great engine with lots of power, and that was my first mistake.
From the day we removed the stock engine was the day we started to have issues. Not once did the old stock engine give any problems. Instead of spending 10k+ on that i would have, should have put that into the handling development of the old girl. It was only after i did start to get that part of the package right did the lap time really improve and that was after i had a 430AWHP engine sitting in it.
Your order of merrit should be something like this.
Weld in cage
Weight reduction program (best HP ever)
Better brake package
Better suspension coil overs, bushes, swaybars and control arms etc
Ensure 4wd system and diffs are 100%
Oil cooler / radiator ( well i had to at least )
That will give you a good platform to start with, and wont cost you a down payment of a house! I like to look at it this way HP will make you a bit faster, as it will cover any mistakes you make or the lack of handling from your car. Penny dropped for me one day following a clio cup car while running another new engine in. Was only allowed to pull 4000 RPM which put me about the same top speed as the clio. Unlike race days where i would hose them down any straight if i needed too. But following this guy for 20 minutes firmly told me my car was not all it should of been as he handed my arse back to me in the twisty sections. But some investment in good coilovers etc and a alinement spec supplied by Giant made far more improvement in laptimes then when i dropped the 10k engine in.