Abb+ lethal assault is viable to lvl up (and endgame too). For cold RR devotions you got : Viper (since you using a weapon skill it is a nice -20% elemental on everything you hit). Murmur and Crown (as you already found out). It’s not that you have to take em all of those three - i usually have murmur + viper as must have-. I wouldn’t go for tsunami but for amathok, it’s a very good one for someone even better than leviathan.
Edit: I forgot to mention had of ultos (flat ele rr) but it’s more a caster thing. It has no place to be in a abb+ la build (imo).
Especially for leveling cold I’d advise eel or sailors guide early on as they have movement speed which is godlike at low levels when you’re one hitting regardless. Of course it’s all flexible depending on your long term plans
I’m currently leveling an infiltrator and it works very well. Get one point in ABB and Veil of Shadow. Max Lethal Assault and Night’s Chill. Get SS for mobility. It’s pretty flexible after that. My current setup (lvl 40) looks roughly like this (it’s from memory): Grim Tools
I headed for execution and got it up to 20% and also invested a couple of points into SS for more damage. Once you get Nightfall and look for oa on gear it procs Blizzard pretty consistently. ABB procs Rumour nicely.
For weapons look for spectral longswords, they drop from ghosts and are also sold by the secret vendor.