I don't feel at all strongly about not calling it a housewarming, but calling it an open house works just as well and if you're on the fence about the term, go with that. People will probably still bring little things for your new home, but so be it. If you're not likely to live in this house for an extended period of time, I'd definitely call it an open house.
Hosting an open house is usually far more casual than hosting a dinner party. Both drinks and food are usually buffet-style; I am generally adamantly against using disposable plates for indoor hosting but for an open house, I don't really mind it. I do think it's nice to provide real cutlery and glassware even if you do use disposable plates, just because it tends to be practically impossible to cut things with plastic knives and forks. If you plan the food so as not to need much cutting, like sandwiches people can build themselves, you won't need much.
Both an open house and a housewarming imply that people can arrive at different times and that there may be lots of guests coming and going--it is not rude to arrive an hour after the designated start time, but when you send the invitations, you send them with a timeframe (4:00 to 8:00 PM) whereas with a regular dinner you would indicate only the start time. (Be aware that the end time tends to be an hour or so later than you actually state.
) If it works in your house, I find the best way to keep people mingling and not congregating in any one area is to have different 'stations'--drinks in the kitchen, food in another area, desserts somewhere else.
Most people bring small items of food--the truly traditional gift for a housewarming is bread and salt--but wine is popular around here, and some people will bring flowers or small household items. You don't create a wish list or a registry for a housewarming. You don't have to open anything that's wrapped on the spot, and you should send thank-yous for any gifts you receive. If people bring items that are suitable for adding to the buffet, you can do that, but most people bring non-perishable items that are really meant for you to enjoy later.
Do not feel pressured to lead house tours, and it is perfectly acceptable to have some rooms off-limits. Yes, the idea is to welcome guests to your new home, but you're not trying to sell it, so you don't have to have open access to all areas of the house.
If you have an outdoor area and it's a nice day/night, having seating outside or grilling things is also a nice idea.