The torque setting will be for the three suspension mount nuts where the strut brace is mounted. I've fitted front & rear strut braces and used the torque settings out of one the the manuals I have (Bentleys, Haynes) but can't recal exactly what the setting was
As for using rubber matting underneath... what for!? The strut brace should not be "rubbing" on the body work, if it is it's fitted incorrectly and won't work properly, nor will your front struts. The fitting must be good and proper, nice and tight. If there's any slack / movement this "play" will be taken up before the strut brace can take the strain! There is absolutely no need for anymore damping, the suspension bush (between the bodywork and strut, which the strut brace is fixed too (the three bolts which pass thru the strut brace come from the bush) provides all the damping necessary and all that's been designed for the car.
Also, your strut brace is different from mine but it may have the same clearance, i.e. limited, that is there's very little room between the top of the strut brace and the underside of the bonnet, adding height through the use of rubber matting under the strut brace may cause it to foul the bonnet. If you do decide to go this way then check the clearance first.
Lastly, when fitting the strut brace take the weight off the front wheels so you can fit the brace properly without having any adverse affects from road camber, etc.
'89 325i - was an SE but not anymore, was bronze-beige metallic (yeuch!) but now techno-violet (thankfully)
'89 Toyota Corolla GTi-16 - track, hillclimb & sprint car (yeeha!)
'08 Buell XB12Ss - American engineering at it's 'best'... good fun though