Some other thoughts on this, note that I am not an architect!
Something with dual extruders might be useful down the line - the TAZ5 has or will-soon-have this ability. You can (I believe) use the Dually mod with the Taz5, but it uses a different nozzle/hotend structure so the upgrade is a bit strange and will probably have you delving into the firmware a bit. I’m pretty sure Lulz is working on a version that won’t need as much firmware mucking.
Anyway, dual extruders are great if you need to do anything with overhangs at hard ( > 45°) angles. You can do support structures and models with a single extruder, but the cleanup can be a huge pain. You need the support structures for overhangs or else the printer will be trying to print in mid-air, and you’ll get plastic spaghetti instead of a worthwhile model. A dual extruder lets you print the support structure parts in a completely different material - usually PVA (water soluable, it’s the same stuff in Elmer’s Glue or wood glue) or HIPS (soluble in Limonene).
I recommend the 5 over the Mini for that reason, and for the larger build area. Models made on the Mini will have to be pretty small, so you’d have to print things in pieces and glue/snap them together to get sizeable models. The Taz5 has a pretty big build surface - one of the biggest, if not the biggest, at it’s price point. You can print pretty sizeable structures with it.
The 5 also gives you a nice all-metal hotend (the Mini might have this, I’m not sure) which gives you a very wide range of available materials (like Nylon, polycarbonate, etc).
The 5 also looks to be easier to modify as needed. I have a TAZ4 that I’ve modified the crap out of - auto bed leveling sensor, custom extruder setup with an E3D dual-nozzle Chimera hotend, stiffer supports, and sound dampeners on all the motors.
The Mini has some nice features as a starter printer - auto bed leveling removes one of the most time consuming calibration processes - and it’s very good for beginners. But if you think you’ll be doing anything sizeable, which seems likely for an architectural firm, I’d go with the TAZ5. It’ll be a slightly steeper learning curve, but I think you’ll get more out of it in the long run.