Okay, I nearly melted down reading this post, so lets dissect, shall we?
I am on a cycle of 450mg of Test and 200mg of boldenon a week. Would it be ok to do cardio three times a week for thirty minutes, moderate intensity?
Short answer: no.
My goal of this cycle is to gain good quality muscle and stay lean 8-10% bodyfat,
You can't gain "quality muscle" at 8% bodyfat. Impossible.
my diet is good, with plenty of good calories.
You don't need good calories, you need any calories you can get, fuck the model look, fuck the jawline, eat like a horse and train, especially since you're using now. Time to stop the bullshit pretty-boy look. You won't get big if you eat like a bird.
Also, a weak point I want to bring up is my arms. So basically can I get away with doing cardio three times a week and if so when, or should I do none at all, and is this a good split to bring up my arms? Will cardio hinder my gains?
Cardio will stop your gains. Don't be a fucking moron, you're playing with your health, might as well do it right, so stop the fucking cardio and hit the weights.