Most of the available 4-digit codes can be found here: http://www.pokemon.jp/portal/member/summer10/code.html
You may require a membership to view it. Also, not all codes are on the main sites, which may require you to click on the links.
Here's what I've gather:
1) You can hold a maximum of 99 for each stone.
2) You do not need to befriend each pokemon to have its data. It is recorded after you've seen it.
After aquiring 30 species, class rank is changed to Junior Class.
After aquiring 60 species, class rank is changed to Silver Medal
After aquiring 100 species, class rank is changed to Gold Medal
After aquiring 150 species, class rank is changed to Red Star Medal
Forest: Out of 106 Pokemon, 96 can be befriended(excluding the 8 legendaries: Celebi, Latias, Latios, Kyogre, Cresselia, Phione, Manaphy & Shaymin).
Lake: Found 78 so far... (Legendaries include: Articuno, Zapdos, Moltres, Mew, Lugia, Ho-oh, Rayquaza, Jirachi, Deoxys, Mesprit, Azelf)