Ask a Vegan Baker

I'm making a batch of cupcakes for a work party and would like to make them vegan since the party is in honor of the one Vegan in the office. I've found a cupcake recipe that's vegan and doesn't call for anything more exotic than coconut milk (since the more exotic the recipe the more spectacularly I tend to fail at it). Now my dilemma is Frosting. My favorite frosting recipe is super simple and produces light fluffy frosting every time and I'd like to try making a Vegan version of it. I've used Almond milk successfully in the recipe so that substitution isn't a problem, my co-worker recommended using Earth Balance for butter in baked goods but I'm worried that the frosting will turn out runny if I just try a one to one substitution.
Base Recipe:
1 cup Milk
5 T Flour
1 Cup Butter
1 cup granulated Sugar
1 t vanilla or other extract

Also, since I'm vegetarian any specific product recommendations for supplies that are vegan or things to look out for on labels that I might not be expecting would be very much appreciated!
Edited to add: I should mention that I have make frosting that were all shortening before and that was the most tasteless disgusting thing ever, and left my mouth feeling like I had eaten an oil slick, I'm trying to avoid that here.