There's an unclassified army manual for EMP-proof facilities design, EP 1110-3-2. All your answers are in there
The amplitudes are completely different between EMP and TEMPEST and frequencies vary a little, but the level of attentuation and design for protection for both is practically identical.
To get 90dB attentuation, you can't just use tin foil, you have to use a significant thickness of steel or copper or another conductor, otherwise a significant portion of the EMP burst will transmit straighit through it and still come out the backside at reduced but dangerous levels. The thickness depends on the frequencies and desired level of protection, and of course the material being used- welded 1/4" carbon steel will provide this protection.
You can buy filters for power and communication lines that provide > 90dB protection.