I think it would be cool to have your character name changed to a different color in the specific guild your in, Also when other players walk by you the name of the guild your in appears on the top of your name so everyone knows what guild your in, It would also be cool to have an emblem like a small pikachu sprite for instance beside your guild name above your character name, And guild coins is a good idea, Rare candies and vitamins could be around 20k guild coins, While like other items that pokemon need to evolve like Reaper cloth magmarizer, Electerizer, Protector, etc could be around 8-10k guild coins, And the elemental stones could be around 1k, and low tier items could sell for 100-500 guild coins, But the items to boost pokemon stats or type moves like inscences like Rock inscence (I dont know how to spell the correct word) they should sell around 4-5k Guild coins, But choose any value you want for the items, Im just suggesting. There should also be Guild battles! Guild vs Guild and then a leaderboard on who is the top guild with the most wins etc.