Regarding older Medium Format bodies

After noticing the prices of older Hasselblad bodies on eBay I thought I'd entertain the idea of getting a medium format camera. I currently have a 1Ds II so I'm not against using older tech and I'm not that fussed about movie modes or high iso.

My question really is is that what would I lose out on if I bought a H1 series body as opposed to a H4 for example(not like I have the budget for a H4D). I am not too bothered about all the fancy stuff most modern bodies will provide and whilst I like having a weather sealed body its not a requirement.

Is there any limitations on using a H1 body instead of a newer body, limits on what backs I can use or maximum pixel count/sensor size etc?