I'm gonna wait for mods to update before I hop in, but super excited to check it out.
A good early trick with the Assassin is to trade in most of the weapons for two SRM6 stacks. You can make it live up to its name by getting close, dumping a decent sized burst, then using its speed to GTFO before coming round for another pass. Especially if you use Artemis racks so you concentrate more damage into a single location.
Accessorise with a short burst or pulse laser in the hand for cherry tapping things that are already exposed structure.
It's always going to be a victim of the 40t curse though. (40/45t mediums tend to be good at bullying things smaller than them but not good at trading with anything else).