The Aillio limitation of 1-2 m was for an unpowered exhaust duct attached directly to the Bullet. Preferably that duct was to be straight (no elbows or bends). I have misgivings about a passive duct like this because of air drag in the duct as exhaust moves to the outside and because air pressure differences between the building interior and the exterior ambient pressure will directly affect air flow thru the Bullet. Make-up air for the room is critical for a passive system in order that the Bullet exhaust fan can operate unaffected. In addition, air movement outside the building can affect the passive flow rate. Now comes too much info…
An alternate is to add in-line, powered air movement with enough flow rate and connect that powered exhaust duct directly to the Bullet. In this case you run the risk of the external exhaust affecting the flow rate of cooling air thru the Bullet. Anything that alters the air pressure at the Bullet exhaust vs. the air pressure at the Bullet air inlet (lower rear of the Bullet) affects air flow thru the Bullet and consequentially alters the air flow for a specific F#. That essentially overrides the Bullet’s exhaust fan.
However, if you leave a gap between the Bullet exhaust and that powered ducting (the range hood you plan to use is a great example), the external system can sweep the air space without affecting air flow thru the Bullet because air pressure at the Bullet inlet is (probably) equal to air pressure near the Bullet outlet. Under these conditions the duct length can be whatever it takes to get to the outside to the extent the flow rate is high enough to move contaminants outside before they condense or attach to the inside of the ducting. @bertje1959 (above) suggests a filter to collect the contaminants which is a great idea.
Assuming you have a source of make-up air like an open window or door, a powered external exhaust system (range hood or a purpose-designed exhaust system) can keep the air fairly clean (it’s not perfect!) without affecting Bullet roasting profiles. Just keep in mind that after you shut off the roaster, oils inside the drum and the exhaust will evaporate and cling to everything in an enclosed space. That’s a vote for keeping the exhaust system running longer than just while you roast.
Also, an air-gap connection is the current recommendation from Aillio.