A 1500 should be fine for you.
Your R730 can be configured in either redundant mode or non-redundant mode for power in the iDRAC settings. If you have it set up as redundant, it will use up to 750W (give or take a small amount for power conversion inefficiency and such) since a single power supply would need to be able to support the entire server if the other went down. In non-redundant mode, you can use up 1500W (again, give or take a small amount) but if one power supply goes down the entire system may go down (I've never personally tried this so not sure what actually happens).
You can also set a power cap in iDRAC settings as well if you want to be extra cautious - this is the maximum power it'll use (give or take a small amount again).
I have a 1500W CyberPower unit that I use for my R730 with dual 750W power supplies (in redundant mode) along with several other things (other servers, networking equipment, tape drives, etc). I draw about 400-500W depending on what I'm doing. I don't use any of the power capping features so theoretically I could exceed the maximum output of my UPS if I were to push all of my stuff to 100% usage but I never do that so it's not an issue for me.
eBay allows sellers to send offers to "interested buyers". My understanding of what eBay considers an "interested buyer" is either someone who has watched the item or someone who has viewed the item page multiple times.