No current templates for Mando helmets. May be able to find some for clone helmets and modify them...check the clone costume boards (clonetroopers.net, whitearmor.com, etc)
As for greeblies, look at the ones on the clones, you'll see raised areas and parts. Otherwise after painting you can apply some paint apps to it to help make it look less boxy.
Here's the progress work on my macrobinocs, you are welcome to leech ideas. I just "winged it" on mine while using the clone macros as a reference.http://mercs.firespray.net/forum/index.php?topic=13486.15