1. Mercs aren't really a faction of their own but rather a pool of units that can be used by certain factions (depending on the individual Merc unit). Some factions have broad access to Mercs however and can be run as Merc armies. Check out Qapu Khalki (A Haqqislam Subfaction) as they have the best access to Mercs.
2. Orpheus beat me to the link. The Gallery catalogue is the best way to look at models.
3. Don't forget the free rules and unit profiles available [URL="http://infinitythegame.com/archive.php"]here[/URL].