Advice: where to start

I think you're best bet would be to try to observe in some of the units you're interested in, if that's an option.
The major difference that I've noticed is that MICU seems to adopt a more "wait and see" approach, whereas SICU is "treat the second some thing even looks funny". SICU patients also tend to be healthier to begin with (healthier being a comparative term, they're still often very sick), because you have to have a certain level of health to be a surgical candidate... for the most part.
A year and a half in... I still like codes, but I kind of hate when the code pager goes off. 50% of the time the patient is fine; sitting up in bed chatting, etc. by the time I get there. 20% of the time they're really a "rapid response" that gets called a code blue because they wanted some extra help... which is okay, but a little annoying. I have my own critical patients to attend to, and if yours are breathing and have a BP compatable with life, I need to get back to mine. 20% of the time they're dead. Old and dead. Let them go to heaven for pete's sake!! If I'm 85 and my pupils are blown for the love of God (and i mean that sincerely) let me go!!!
And then 10% of the time... there's no pulse, the code team gets there. You push some Epi, do some compressions, intubate, push some atropine, etc. etc. and there's a pulse, a BP, you get the patient to a unit and Yeay! You've saved someone's life. Happy day! That seems really rare though.
I don't really have any tips for trying to get into a CCU. If you have one at your current hospital, it might be a good idea to apply there instead of M/SICU though.
Good luck!