Critique My Easter Menu

HELP! This is my first time hosting a big family meal and I want to get it right.

Here are the facts:
1. There will be 8 people attending dinner and 12 people attending dessert.
2. 1 of the 8 dinner guests is a vegetarian.
3. I can't change the main dish because my mother-in-law has volunteered to bring it.
4. Since it's going to be pretty warm, we were thinking of eating outside.

Appetizers
Bleu cheese, chopped walnuts and tawny port spread (my husband's grandmom will be bringing this)
Hummus with crackers, carrots and cucumbers

Salad
Chickpea Salad from Kalyn's Kitchen

Main Course
Heavenly Ham (from mother in law)
One Portabello mushroom for the vegetarian
Grilled Pineapple
Asparagus with a balsamic glaze
Corn
Potatoes

Dessert
My husband's grandma is bringing a cake
My mom is bringing an ice cream cake
Coffee
Tea

So, now that you've seen the menu, here are my questions:

1. What kind of potatoes would you make? mashed, baked, those little red roasted potatoes with rosemary?
2. I've never cooked a portobello before because I'm not really a fan of mushrooms. Have you made one and how did it come out? Do you think I'd be better off grilling it? I found a few recipes that say to grill it instead of bake it.
3. Am I missing anything?