Like orvi, I have no experience with manufactured hoods either. Because of my work area I had to make mine in place to fit where I wanted it. If you find a fume hood but it has metal hardware, you can possibly purchase plastic/Teflon replacement hardware. Using marine grade 5200 sealant over fasteners/small hardware would slow the corrosion down, but Hcl fumes are pretty intrusive and will find it's way in....eventually.
The fan motor/blades/lighting fixtures would probably be a constant issue depending on it's placement in the system. Seems like every year I have to replace my "sealed" light fixtures because of internal corrosion. So far my fan motor hasn't failed.....yet. I do have a spare motor/power supply just in case it fails during a reaction and it can be replaced in about 5 minutes.
When set up with the "chimney" thing, you can cleverly put the motor at the end of the pipe, after the scrubber part, to greatly prolong it´s life. Some aerosol separator mesh or something similar needs to be placed after the spray nozzles of the scrubbing part, not to dampen the fan tho.
Yeah, HCL find it´s way to practically anything. Altough putting some protection on the bolts certainly helps a lot. And if you cannot wash the chlorides off of it, it will corrode till no metal is left.
Actually speaking, metal is thing of issue. As far as you go with plastic, or even hard wood, you will be served much better.
My opinion is, it does not need to look nice, it just need to work as it should and be durable enough to not fall apart. Few plastic sheets, I found some fiberglass resin ones... Plexiglass for the front "door". Even asphalt soaked roofing material is OK for the walls, but I will certainly use something more durable... But I seen it personally to be used and it worked as it should. Piping from foldable PVC sleeved air conditioning "tube" is perfectly OK for the exhaust - cheap, flexible, non-flammable, nice resistance to NOx and Cl2 gasses, easily replacable if needed. Chassis of the hood, I seen built from the plastic/sawdust composite "timbers" (which are relatively nice as they usually contain fire retardants) bolted with plastic screws. As long as it does not need to support any weight from the top, it is perfectly OK. One folk has this exhaust tube lead through old and unused chimney all the way to the top of the roof - nice adaptation from my point of view.
And as you very wisely pointed out, you should be able to easily and quickly replace the fan on the hood in case the used one dies down. I seen by-pass made on the end of the exhaust tube, which was sealed from the fumes, with "emergency" fan mounted. If something goes wrong and motor dies, you can switch the other one on in matter of seconds to save your work and health