you can run it that way, however, you are not using the FB efficiently, ie if your offset doesn't have inlet vents then the door should be "cracked" but not wide open for the majority of the cook. You will use less wood that way.....I run the stack wide open and for 99.9% of the cook yesterday I left the firebox side door open all the way. Only closed it a bit a couple of times when the cooking chamber temp started to climb a bit too much.
I Agree with civilsmoker, if you have to many that aren't burning hot enough, it can cause dirty smoke, but sounds like you had it handled. Then just finding your balance for intake and exhaust.However, if you get TOOO MANYYYY coals you can start to oxygen starve the bed and can degrade the clean heat they offer.
That's the name of the game with an offset...... keep the coal bed active. When you loose your coal bed the cook is over.While cooking yesterday, I kept the temp in the cooking chamber between 250 and 265. After cooking for about 4-hours, I noticed that the coal bed had grown quite large. Is this normal?