Caitlyn

1 - In my opinion a reasonable DPS number for a MCH with ilvl 170 should be between 550-600 DPS. Now, a good MCH would go over those numbers obviously. But, if ur DPS is around those numbers I just said, then u're doing ur job to DPS bismarck down

2 - I don't believe there is a best in slot right now, only because you have no gear to choose from. There's only one and is that one you have to get (in this case being the Law/Centurio Seals gear)

3- At the moment, I believe GB should be use with ur Opening or at any circunstance where you can cast it without loosing any DPS. For example, when a boss is invulnerable because of some ability-animations he does or whatever. In the end, you would want to switch between GB when u have a window in which u cannot make DPS. Eventhough its all circunstancial

4 - In that case, if u have GB up, use Feint and Gauss Round when it pops. If you dont have GB up keep spamming split shot cuz at least Quick Reload should be coming up soon