Ideally, it is best to keep a hall clear as it lets the positive energy flow through although if the stool is small, this should not cause problems.
Daniel on Feng Shui and Mirrors
If possible, I would put a circle around the number 4 on your company logo as you suggested. 3429 is considered a good number as it adds up to 9 and I would not worry about this number.
Daniel on Feng Shui and Numerology