Alrighty here are my ideas...
Roster:
-Mario
-Luigi
-Peach
-Daisy
-Yoshi
-Birdo
-Wario
-Waluigi
-Toad
-Toadette
-Rosalina
-Pianta (newcomer)
-Nabbit (newcomer)
-Shy Guy
Stages:
-Acorn Plains: A board based off of NSMBU's Acorn Plains. Get the stars for 20 coins the classic way!!
-Gloomy Manor: A board based off of Luigi's Mansion: Dark Moon's Gloomy Manor! Plays similar to King Boo's Haunted Hideaway, with the innards changing from the 5 different themes of the mansions.
-Peach's Birthday Cake: A board returning from Mario Party 1, and plays very similarly.
-Comet Observatory: A board based off of Super Mario Galaxy's Comet Observatory. Chase down Lumas holding treasure chests, which could contain a star, coins, or a launch star back to the start. (Similar to Neon Heights)
-Neo Bowser City: A board based off of Neo Bowser City from Mario Kart 7. The rules are simple: Chase down Metal Mario in the day to get a free star, but avoid Pink Gold Peach at night to lose a star/coins.
-DK Stone Statue: A board returning from Mario Party DS, and plays very similarly.
-Bowser's Gnarly Party: A board returning from Mario Party 4, and plays very similarly
-Rootin Tootin Town: A western board that plays similarly to Windmillville.
-Wooly Egg: A linear board based off of Yoshi's Wooly World, and plays similarly to Pagoda Peak. Climb up the egg, and each turn, a baby selected at random will be there which will determaine the cost for the star...
-Baby Mario: 20 Coins
-Baby Luigi: 10 Coins
-Baby Peach: 30 Coins
-Baby DK - 15 Coins
-Baby Wario: 40 Coins
-Baby Rosalina: FREE
-Baby Bowser can also show up and STEAL A star or coins.
-SECRET BOARD: A classic themed board which takes place in a museum with artifacts from previous Mario Parties. Collect a star for 20 coins.