i have a yugo kit with a good bore but light rust in the chamber. the metal is covered in cosmsoline. i was thinking of removing the wood and dumping the metal in a bucket with mineral spirits. i know this will remove the cosmo but what about the rust? will this harm the blueing? any other chemicals to consider? how do you prefer to prep a kit to build?

I used mineral spirits to clean my kits, melts the cosmo off the metal pretty quick.  I cleaned 5 kits with maybe a pint of mineral spirits and a brush.  
Rust in the chamber????  mmmm, I would get after that pretty quick with a oversized brush and 4 ought steel wool, soaked in any commercial gun cleaner or rust remover.  You want that outta there asap.  Flitz metal polish always removes light rust without much effort, I keep some around the house all the time.  

i heard you can use one of those little stemers you can get for like 50 bucks they say the casmoline just drips right off with it.

I use plenty of heat to remove cosmo from the metal and wood parts of rifles.  In the summer time, I place the rifle in a black garbage bag and let it lay in direct sunlight.  Melts everything off.  In the winters, I steal my wife or my daughters' hair dryer and apply heat to small sections at the time while wiping it off with a rag.  I found out that Simple Green also helps to remove the cosmo from the metal.