please confirm this so i can go ahead and buy it
I'm not entirely sure with what you want - we gave you our recommendations and showed you that the total consumption of the system should be in the 150-170W range. Is 150-170W less than 250W?
No one here can guarantee that you will have zero issues - any time you open the case something could happen. Any time you deal with hardware, something could happen. The card could be DOA. You could have a faulty PSU that's only putting out half of what's on the label. Your PCI-e slot could be broken/your mobo could be faulty (since you've never used it before). You could forget to ground yourself and short the board when you touch it. There was even a guy on here once who, instead of unplugging the PC tried to unscrew the power socket from the back of the PSU and fried portions of his system (which actually was the best outcome there - he could have been electrocuted). None of us can assure you that these things absolutely won't happen. The best we can do is say that "based on my knowledge and experience, in your situation, this is what we would do".
And that's what we're saying. Sorry about the rant. Buy it or don't - you have the info.