With light you get faster running speed and more evasion...but thay are realy not really perceptible. Since you are an orc you evasion and speed really much suck either way.
As a Tyrant the bonuses from Light Armour definitely help. The 10+ speed bonus from wearing light helps (when using Wolf and Rabbit Totems) but I agree that the evasion doesn't make much of a difference.
As long as your not tanking for a group or if you have VR, Plated Leather is a fantastic set to have.
As for c grade if u can afford it go Plated leather set. (Vr is essential though). If u are poor go composite. As for weapon certainly risk haste great patas win :)
For me patas on my server are rare, maybe an alternative and something i used alot bck in the day for my Tyrant was the fist blades /with haste. Very good weapon to have way into ur B grade.
PS i talk from past experience like C3 and lower, perhaps things have change to much for this info to be valid...
One of the big changes is the ability to upgrade and exchange weapons in D and C grade. This means with AA you can get pretty much any weapon in D and C grade (there are a few exception like Demon Fangs).