Well, from that picture we can gather that they are light-skinned and have rather powerful and strongly-marked features - possibly deep-set eyes and strong brows.
Perhaps a middle-thing between a white Brutor and a Civire.
Their cultural style would likely be no-nonsense and as practical as possible, but more in a "that'll do"-sense than what you might find among the Caldari. Where a Caldari technician might have a highly-advanced self-lubricating multitool that works on all Kalaakiota and Sukuuvestaa equipment, and wear a pair of pants with pockets specially designed to carry that type of tool, a Thukker would bring a spanner and a screwdriver in a toolbelt he had to make himself from an old jacket.
Thukkers would likely regard the idea of "high-class" as something alien and rather abhorrent. If you're taking up more space than someone else, you'd better have show each day that you deserve it - and it would be out of the question to dress like you're better than anyone else. The tribal structure with caravans might have a certain social stratification reminiscent of the Quarians in Mass Effect, with the captains of vessels having certain representative rights within the caravan, and possibly some sort of tribal/clan/vessel heraldry to display their authority. Possibly tattoos rather than dress uniforms, allowing one Thukker to read another's service record on his skin:
Line one: Harek Milgenson, Thukker of Caravan Dragan, born on the Iskender
Line two: Served on the Hymla, the Sable II, the Orm, the Yggdr
Line three: General Mechanic, Battleship Engine Maintenance, Reactor Engineer
Line four: Husband of Ulva; Father of Milgen, born on the Orm; father of Anha, born on the Yggdr
But that's all conjecture. Until we actually get to see Thukkers in-game the details will likely be rather fluid.