If your going for max bodies I'd loose the chosen. As a general rule you want to preserve your expensive units (depending on a ratio of cost per model vs toughness) and try and force your opponent to deal with cheaper guys first. Putting chosen in front will probably end up in the chosen doing all the dying early on and being outnumbered in CC.
Instead, have your elites deep strike or come up behind your large squads (in 5th ed. when LoS is blocked by your own squads.) Also, your infantry are going to take a lot of punishment running across the board if your facing a shooty guy. Take icons of Nurgle or Tzeench! They're expensive but points per model is really reduced when your taking 20 guys per icon! It's going to be difficult to cause moral tests with shooting when you need to kill so many guys, especially with invul. saves or toughtness 5.
For an HQ, realize your going to be shot at a lot in many cases, so a statured HQ will be a target of priority. A really choppy lord or sorcerer would fit the bill. Consider a sorcerer with LoS to make up for your lack of speed, or a special HQ. So many of the best HQ's are on foot, like your army will be. Kharn comes to mind immediately. Whatever you do I think a strong HQ is in order with so few powerweapons around. Awsome mounts like the Kornate juggarnaught and nurgle palinquin are often not used because they cant keep up in most lists but you wont have that problem.
Elites are mostly up to you. Termies are a good choise cause they wont start on the board and make up for a lack of powerweapons too. Most likely they arent going to be late to the party since your taking the long way with your infantry.
After that all I can say is you may be in trouble against mech armies. Meltas wont cut it with such slow units. You can probbly afford two or three backup heavy weapons to help you deal.
