You should get a few different kinds if you are recording a variety of them quite often.Get a dynamic mic like the SM57 for capturing the attack of instruments.The blue mic might do a good job with its amazing headroom. Have a small diaphragm condensor for strings.ONe good mic would be the Rode NT3.If you want a stereo pair,get the NT5.I've heard good things about the C1000s thou.
The last one you might consider getting is a large diaphragm condenser.This can be used to capture the ambience sound.The beauty of the instrument.If placed properly,it can make your instrument sound larger than life.THere are so many great LDCs around.The baby bottle,NT1a,KSM32,TLM 103,Luna,etc.It all depends on your budget here.