I'm not a fan of Atlas Copco at all. Some parts come from overseas with a long delay, and their reliability isn't always the best.

Used is probably not a good idea unless you know the complete history.

For 8 hrs/day commercial use you may not need a variable speed model, those pay off in energy savings for 24h industrial use. But there isn't much downside if the price is right, its not like electricity prices will ever decrease. Depending on what it costs you for downtime, it may be worth considering two compressors so you have redundancy. Each would be capable of 100% of the flow, and a cable between the two so they alternate.

Add up you expected air usage carefully, and keep in mind that compressors at altitude need special consideration. Besides getting it sized right there is also cooling, compressors give off a lot of heat and thin air carries heat away less than at sea level. You can't stuff the comp in an un-ventilated closet, it needs a lot of air to the cooling fans and likely some ductwork to prevent short-circuiting and keep sawdust away. Also keep in mind the routing for the pipe out to the intake filters.

Sizing the receiver is important too. Don't skimp on accessories like the drier, coalescers, particulate filters, etc. It may be cost-effective to divide up the treatment system, general tool air is split off from before the extra equipment used to get the quality right for paintshop air.