For 3) - For a party, I find that the best thing to do is prepare a variety of foods. Have some stuff that is vegan (which also handles vegetarian, lactose problems or kosher/halal restrictions), some that has no nuts, some that's wheat free, some that's soy free. Label the 'safe' items. That way everyone can find something to eat without you having to obsess over the details.
I live in an area with a lot of vegans and vegetarians and my family has issues with allergies. Seeing all of the delicious looking and smelling food and not being able to eat during a dinner party is not fun.
As for computer use, I do urge setting it up so the speakers are a part of your party, but not the computer if at all feasible. If people are tempted to browse the computer it might help if it is out of sight or in a non-public area of the house.
And my family are landlords, so while extra coat racks are great (especially in winter), do try any adhesive products out in a less obvious area and try to clean them up as soon as possible. The next tenants and the deposit will thank you.