You should be fine, website says a 400W minimum on that card. Doesn't give you a lot of headroom for future upgrades, but it will definitely work fine right now.
Yes, you're fine. Assuming the PSU is of reasonable quality (e.g. Dell), it probably has a PCIe power cable and can run a HD7770, HD7790, or GTX650Ti [Boost Edition]; possibly others.
You should be fine, website says a 400W minimum on that card. Doesn't give you a lot of headroom for future upgrades, but it will definitely work fine right now.