I've been looking to replace my native kontrol s88 mk1. Partly because the keybed makes a lot of noise, partly because native instruments ceased to support it and partly because the action is not that great compared to grands I have access to (Kawai at my teacher, yamaha disklavier at a friend).

So I've been looking at different digital pianos. After testing, the best I found in term of both feeling and sound is the Kawai CA701 and CA901. There's only about 700 euros difference where I am between both so I'm leaning towards the CA901. I do have a few questions:

1. I won't be able to have a big gap from the wall. It'll be around 5-10cm maximum. I know that this will impact the soundboard but I'm wondering how much. I read that Kawai says 3.5 cm minium is needed with Wall EQ. I just want to confirm if a CA901 that's 5 or 10cm from the wall will sound much better than the CA701

2. I plan to also use VSTs and output the sound back to the speakers. I've read that using usb midi with audio sent to the line causes ground loop. Any effective way to mitigate that?

3. I live in a place with a very humid climate sometimes reaching 85-90% inside the house. Will that be problematic for the instrument?

4. It seems that where I live (HK) the warranty is only 3 years compared to 5 years in other countries. How often do problem appear between year 3 and year 5?