Im decluttering - how ruthless should I be? I dont want to regret getting rid of stuff but want less clutter!?

You have to be a bit ruthless. If you haven't used it for 6 months to a year, it has to either be donated to a charity or have a garage sale if you are so inclined. Garage sales are a lot of work and usually for little return but if you decide to have one, make sure what doesn't sell doesn't come back into the house. Take it directly to a charity drop off. Important papers need to be sorted through and some need to be kept for at least 7 years. At least in the States for possible audit purposes. Find appropriate sealed and stackable boxes for those items. It's amazing when you start to go through stuff how much you carry with you that you just don't wear or use. It's important to do this yearly so it doesn't get away from you again.