It looks like the most heat in that case will be on the two sides that have the pairs of MOSFET's mounted on the aluminum plate. Another area for greater heat is usually adjacent, where the string of driver transistors and resistors are located.
When reaching for ultimate heat dissipation, the area contacting the transistor junction and immediately adjacent is where the most transfer occurs. That is why you will see fins on heatsinks, so the junction temperature can be dissipated immediately into the small fins. I mess around with this stuff, installing a single pair of mosfets onto 12" x 3/8" w/2" fins x 7" aluminum heatsinks, for example. Sometimes I use copper spreader bars and all other manner of thermal interface materials. At 25 amps, there will be some significant heat being dissipated. You seem to have a good handle on what to do.
Panasonic FC capacitors at Digikey (for Mex).
