The Ebony Mail (Beothia's Calling) only applies muffle on the armour itself, not the rest of your gear. The way that it shrouds you in shadow and poisons enemies who gets too close is awsome though. Not for archers though as the shroudin effect gets in the way of aiming at targets. Dark Brotherhood Shrouded Boots or Nightingale Boots will muffle all your gear (not sure how well if works with heavy armour though. Since you're aiming to be an assassin I presume you'll join the DB and will then defnitly use the gloves from the Shrowded Armour for the backstab bonus. Which leaves only your head for which you might as well add the DB hood to give you 1 x heavy armour and 3 x light armour pieces.
If you really want only heavy armour try to get the enchants for fortify sneak and muffle as early as possible and put some perks into enchanting so you can make some good quality enchantments.
If you use the Steed guardian stone you don't need any perks in heavy armour except Juggernaught. and Well Fitted. You also do not need the muffle perk from Sneak as this is provided by your DB/TG boots (unless you want to go full heavy armour of course).
Personally I prefer light armour and medium HP to keep things interesting. I mean what's the use of sneaking if you can go head to head with a giant? If your life depends on remaining unseen and unheard then every dungeon becomes a fun game of cat and mouse with the mouse hunting the cat.