10 plague marines is over kill. 7-8 will do. saving you 40 - 60 points. Thousand sons need to be at least 9 strong, just because you don't want a job half done.
I was wondering about the numbers in the previous post. I guess a 10 man unit would be more cost effective (in terms of money as well as points) for stepping up my army. Plus I've got some rhinos I can cannibalize from other armies. I think I have a few Tsons around here somewhere. Hmm... I may not need to buy anything for this next step. Have to do some looking and bitz box diving. Now then, where is my JIM suit