I kinda of like the Rayman (the 1st one for PC) style, where you go through levels and you usually can't get everything the first time around. As you gain new abilities along the way, you can go back on the world map to replay levels and use the new abilities to reach places you couldn't before. So it's a lot like SMW style except for the new abilities allowing further exploration in previously played areas.
My second choice is to go with the "Great Cave Offensive" way, which I like almost as much as the Rayman style.
As for the number of mushrooms, it kind of depends on the way the island is mapped out as (world, areas, levels). For the Rayman style, I'd like 7 normal and 1 golden per area. Otherwise I'm just going to agree with Dark-Hylian and say about 50 or so with 5 or 10 goldens.