I'm looking to see whats the limit of characters a nxt message can contain.
In V1.5 this has been increased to 42K but your message will be pruned after 14 days leaving only its hash. You can still store permanent messages 1000 bytes long but this is likely to be reduced in the future.
Right now it's 1000 bytes. Text is converted into bytes by using UTF-8 encoding.
Don't hardcode this limit, use "maxArbitraryMessageLength" parameter returned by "getConstants" API request.