No such thing as a stupid question! I'd always use an old brush for washes. I've read that capillary action can pull washes up the bristles and into the metal collar on the brush. Over time that can damage a brush. Almost certainly no need to buy a specific wash brush though!
Yeah, him! Not really surprised, I just wish they'd come up with a better fluff justification for not allowing tartaros to take shields.
Anyway, I'll probably end up building a unit of tartaros with shields, just because they'd look awesome.
No tartaros armour? Really? Apart from anything else, there's a picture of an imperial fists terminator sergeant wearing tartaros armour in Conquest, page 160.