I have a N73. I heard that 1GB cards are the maximum it takes but my friend bought me a 2GB MiniSD and it worked fine on my N73. Dont go for brand names though cos they are very expensive. The one my mate got me was £30 or something.
The headphone jack I am guessing will be the same as on all Nokia which is a nokia only headphone jack. You cant plug your typical 2.5mm in it. You will have to buy a specific nokia headset.
Hope that helps.
Mark