Welcome to AVS! The first advice I'd give you is to read as many of the build threads as you can. There are pearls of wisdom in many of them, often from industry experts.
As for your two questions:
1. Wiring diagram. I don't have a full wiring diagram (actually I'm not sure what you are looking for) but basically there is the electrical wiring, the AV wiring (speaker, HDMI, etc), the control wiring (CAT5, IR, etc). I do have a "design" for the electrical wiring which I used to ensure I wasn't overloading any particular circuit:
2. HVAC. I'm not an expert in HVAC design. I'm sure there are things to take into account in humid tropical environments -- I'd start by reading local building codes and regulations. Once you are familiar with that you need to consider the capacity of the HVAC system (pay attention to the maximum velocity of the air flow) and the need to soundproof (prevent sound from the theater escaping and to prevent ingress of sounds from surrounding rooms).
I'd recommend reading the first post in the Dark Knight Theater
thread where CJO indexes an impressive array of reference material. There are a bunch of links regarding HVAC.
Feel free to ask specific questions.