Balloons - we opted for white Eagle Scout balloons from the Scout store with white curling ribbon. We kept them low and around the perimeter of the room, rather than as centerpieces (except on buffet table - those we flew higher on the table ends).
My number one best piece of advice for you all is: Start before you're ready. Stop waiting around for that illusive feeling that you have exactly the level of skill and organisation that you'll need. Don't hide the link to your Etsy store because you've only got 5 items listed, or not start creating because you haven't got a long term plan. If you wait for that perfect time when everything is right... it will never happen.