SunForce 1000w PSW inverter a couple years ago came with two 500w receptacles, so you can't get 1000w on any one receptacle.
Many other brand inverters have it so you can get the full rated watts from one of the receptacles. That is what you want/need.It matters! Confirm with their tech support before buying which way they do that.
Big inverters draw more amps to run the same small load like a TV set than a smaller inverter would to run the same load. However not much diff between 600 and 1000 for that. Be a diff from 300 to 1500 though.
IMO get a 300 now to watch TV, and then wait till you need a big one to run the microwave or whatever. You have no installation requirement with a little one to watch TV. Just stick it in the 12v socket provided in the Winegard panel.