That 300W motor seems like a DC motor with an ER11 chuck installed. The spindle motors most people talk about here are the watercooled 3-phase motors meant to be used with a matching VFD (which usually doubles the total cost), and are usually 0.8kW, 1.5kW, 2.2kW and up.
IMHO a Bosch Colt 1HP router would be a wiser choice than the 300W motor, it's not too expensive and has adjustable speed. For circuit boards it would be good to get a precision collet kit for the Colt as runout is critical when doing fine traces like those for SMD.
Even the chinese watercooled spindles will most likely be better than most (or any) routers in a similar power category, though.
Can you show us some photos of the machine? It's not clear what's the steel/aluminum for (structure, rails?) and how it's used.