I would suggest starting out with the
AM codex and work up from there.
I heard recently that the "Vendetta" had some update to make it all nice again (if you are willing to convert a Valkyrie or get the
FW kit).
It seems the "new" emphasis is getting some (primaris) psycher and air power on the table these days.
Making good use of our good buddy "Pask" is worth looking into too (Leman Russ Punisher with a full
HB load-out).
Using conscripts with a priest makes for a cheap and hard to kill meat shield for the tanks.
A 5 man squad of Tempestus to deep-strike in with melta is a good armor killer if something really needs to die.
Veteran troops with melta in Chimeras are the "new black".
A few vets sitting back with lascannons (BS4 is key in this case) and some orders can be handy while under cover.
I would suggest Armored Sentinels with plasma because (BS3 sucks and S7 Templates have good utility... plus these guys are CHEAP on points).
For heavy artillery, the Wyvern is worth looking at for addressing horde armies or troops in general.
Cheap! and more re-rolls than you can shake a stick at.
For utility, I tend to field the Leman Russ Exterminator so you can fire everything: S7 Hvy:4 Twin-Linked is not to be sneezed at never mind all other weapons can be fired fully (not ordinance). Can be anti-air in a pinch.
Bringing some Aegis defense lines would be handy for your foot sloggers to hold the line.
This might be more than you asked... I got all excited there.