Ok, very rough calculation, One of those light fittings if mounted on the ceiling at 3 metres producing 3240lumens, would give about 1080lux at “working height” which is roughly 1.2 metres above finished floor level. (4000k cool white)
The beam angle of the light is 63 degrees, so the lux will start to drop off beyond the light fittings “sphere of influence”, so to speak, so positioning of the fittings in relation to each other will be important.
The recommended lighting level for an engineering workshop which is as close to what I think you are after is between 750-1000 Lux.
The colour of the walls/floors will have an effect, but will change once you have placed stuff on shelving on the walls, and have a car or two in the garage.
As for painting minis, you may need up to twice the amount of lux.
Yes I would still go for IP rated fittings, one thing that is missed, is that the building may well be covered, but if it is unheated, condensation within the non IP rated fittings will be a factor.