Ok, if you want to use some very detailed minis, then I think you need to look first to the minis, then try to see what fits your playstyle.
You already play one of the all metal forces (Deamonhunters) and a second strong all-metal force is Witch Hunters. Those are some of the most detailed minis that Citidel makes, but since you already play one of those, you probably aren't all that interested.
Another strong option you have is found in the Imperial Guard. The Vostroyan Firstborn have tons of detail, and would make some wonderful infantry for an Imperial Guard force:
Also, you can probably get some of the other older
IG minis, like the Zulu-wars style Preatorian guard.
Other options exist in the imperial guard too. For example, you could use Necromunda miniatures for guardsmen (this allows everything from the Van Saar's high tech look to the House Cowdor/Redemptionists look - making a beautiful religious zealot force.
The last option with the guard- the one that the most people don't even let themselves think about- is to go ahead and customize every last guardsman. This works really well if you can get yourself some bitz ordered parts (like Necromunda heads) and do a little green stuff work on all of your mini (it is far easier than it looks). Also, I've seen some wonderful things happen with a mixture of Cadians and Bretonian men at arms.
As far as playing goes, the
IG is a pretty strong force. They can even bring in allies from the Kroot or the Inquisition.