I have a A10 7700K processor and i want to make a crossfire with r7 250 or if its compatible 250x. I know the recommended gpu for 7700K is r7 240 but i saw systems that run r7 250. And i was wondering is it possiple to crossfire with r7 250x?
No, only the 250. You're better off disabling the IGP and spending the very little extra money on a 260 and you will have higher performance than a Dual Graphics setup.
It wouldn't bottleneck, and "my PSU is 500w" is about as helpful as blowing on a house fire, as it could mean anything from a $10 Chinese Firecracker which couldn't manage 300w to a high end quality unit. The 260x can pull a meager 125w with mild overclocking, so unless you do have one of those ticking timebombs, you'll be fine.
NO. See how +12v is only rated at 360w peak? Means you effectively have a 360w PSU (basically in a modern system USB is the only thing which uses 5v, PCI and minor PCIe for 3.3v). That's a recipe for disaster if you use a 260X.