I can confirm that you can get an attack chain of Seismic Smash, Stone Mallet, and Heavy Mallet - regardless of the AT, but you will need a ridiculous amount of recharge for that to be the case. I would recommend deciding some other action to use so that you can do
Seismic Smash -> Stone. Mallet -> Heavy Mallet -> Stone Mallet -> Other Action (Reconstruction or Fault as examples).
Fault to me was extremely valuable only because Tremor takes forever to cast (a whopping 3.3s)...and regen loves having sets that mitigate damage so stone is a valuable pairing.
Building slow/-rech is difficult because it's going to disrupt full set bonuses. You will need to slot the unique winters gift and also have 6 15% slow resist bonuses from the winter sets. Splitting up blistering cold by sets of 2 is a fairly easy way to get some. But it will be a super tough time in getting a full build that have the def/res/hp/rech and -rech resistance that'll be good. Not impossible, but most likely very tough. Main priorities are probably going to be Max HP/Rech/-Rech Resist. Defense and resist are great to squeeze in whenever possible.
Something I've done on my claws/fire brute is shaving off some recharge and relying on Force Feedback procs for +recharge as well. Getting to ~150% global recharge and getting FF +rech will let you perma hasten. Gives the build some more room for other bonuses such as the amazing -rech resistance