Just a couple things to keep in mind. First, using CrIm means you're magically creating sounds, not 'throwing' your voice to the target. This means you must roll Finesse to make the speech reasonably intelligible. I'm not sure about the difficulty of the roll. The other thing is that this spell will create speech that can be heard normally by people in your target's immediate vicinity. You can avoid this by using 'miniatures', an Imaginem concept described in HoH: Societates. In brief, you change the Target from Individual to Part and create your speech directly in the target's ears, so no one else can hear what you're saying. This concept can also be applied to other sensory organs.
You would hear any sounds created by the target, but nothing in their vicinity. The only way I know of to hear (or see) what's happening around the target is to use Target: Room, which would then only work indoors. This problem irks me greatly. 
You can, but it's difficult. The ReVi spell Maintaining the Demanding Spell will maintain the Concentration spell for you for a Diameter, or you could just invent Diameter duration spells. There's also a caveat somewhere that says you don't need to make Concentration rolls if you're performing the task the spell is designed to perform. In other words, if your Concentration duration spell creates speech, you won't have to roll Concentration just to 'talk' in this fashion. You would have to roll to cast another spell, though.
Correct, you can't learn both in a single season. As for the two-way spell, I've tinkered with that and haven't found a good solution. Vocis also has a couple spells from the Net Wizard's Grimoire that theoretically allow it, but I think the troupe has ruled they shouldn't work as described.
See comments above re: CrIm speech. You can avoid the Finesse requirement by using ReIm, but the spell level will be much higher.
Have I mentioned that I keep getting Antoine and Lucas confused for no reason at all? 
