you will find plenty of shorter breaks with the santa companies but most of the other 'ski' companies are usually for 7 nights
have a look at espirt for shorter breaks but also inghams do shorter santa breaks without the santa stuff included
if you can go for 7 nights then look at inghams and crystalski
if you want to do independently then you will need to get connecting flights in helskinki with companies such as blue1 or finair - also do look at norwegian air as they fly to finland - you will find the flights will be expensive for that time of year
as for what board you want, it really is a personal choise, it does not have to be expensive to eat out but if you go full board and dont like the hotel food you are somewhat tied
you need to work out where you want to go first and then take it from there