Two quick questions for the chaos enjoyers

**So I had a crazed thought about an army theme. My idea is to make an army that was lost in the warp, with a single surviving space marine tuned chaos, The rest being mutated. using only one "real" chaos space marine, and have the rest of the army be accursed, traitor guard, obliteraters, chaos spawn and such.

Now for the question. First am i even able to do a single marine csm list? Im asking cus i know that there is the you can only have x amount of non Heretic Astartes units rule.

If able I have a second question. I fell in love with the Vandoth the Fallen model. Would i be able to use him as a proxy for a Chaos Lord in Terminator Armour? Like would he be close enough without kitbashing in terms size and armor wise? The datasheet looks like its no problem**