The way Mir3 Differs from Mir2 client side is bascially we are limited to Mon 1-20 and Dmon, each holding 10 mobs. Armours, you can only do 8 in total, not sure if client or server side is restricting this tbh. Weapons again are limited to files 1-5 and each weapon take sup 3000 images - think we have hit the max wepaon wise, case of dropping one in favour of another.
Its on your Paper doll is not limited (phew), horses are limited to 3, Maps - as no mapmaker atm, means limited to what Wemade chuck out. The Spells are all working as per Euromir3 of old, in game email, quests and loads of other things to wet your whisle.
As regards setting one up, the biggest problem is MS_SQL, a lot of people struggle with this and often you will struggle to get server online without it chucking up errors but many have, so it is possible. Mir3 also takes up more Ram then mir2, i would suggest a seperate machine with 1 GIG ram just to run server + SQL.