I am a beginner as well and just gotten used to linked turns. What slowed me significantly on learning the linked turn is that I was lazy on the toe edge. Most of my practices are done with heel edge, and when I try to control my speed I automatically resort to heel. I spent 2 days trying to master linked turns to no avail. But I did realize that my lack of toe edge practice was holding me back.
So I devoted an entire day to just toe edge, till I am as comfortable with that edge as my heel edge. By the end of the day I was linking consistently.
Speed was scary at first because I panic and no matter what position in the turn I am I resort to heel edge by instinct, but once I got toe edge down it was no longer an issue - since I no longer have to do a forced turn to heel edge to slow down (gaining more speed in the mean time since it took longer).
As for your board, it is HUGE for your size. I am 5'10" and 160 and I only use a 156.