A lot of these questions are very basic, so you definitely need to read through a lot of the material on the forums. Read everything in the guide sections, and read other peoples' worklogs. From the looks of it, you should probably read the beginner electronics thread too. I'll try to answer your questions though. Also, don't double post. edit your post if you need to add something.
1. How to wire an hdmi port from the motherboard.
You would have to use an adapter because the Wii does not output native HDMI. You will need something like a Wii2HDMI so you can convert the Wii's component video to HDMI. It will add bulk and not be exactly easy to wire, I've heard Sewell is the recommended brand.
2. How to install Internal IR strips for wii mote.
You just connect two IR LEDs to power inside the case. There's no data which is sent from the Wii to the LEDs.
You'll have an audio amp, you connect the + and - for each speaker from the amp.
4. Battery notifier (meter/ 4 LED monitor)
Not exactly straight forward, you could use something like
this for a low battery indicator.
5. Power Button (Sad I don't know this)
You connect the battery positive output to one end of the switch, and the input to your regulators to the other end of the switch. Read the custom regulator guide for this one.
6. Volume slider & audio jack
You'll need a switching headphone jack, search eBay. For volume adjustment, you'll connect buttons/slider to the adjustment on the audio amp. Note some audio amps only support buttons and not a slider.
7. Screen Hookup (Sad too)
Connect video output from the wii to your screen's video input. You'll also need to supply power and ground. Read through the trimming guide about video output.
8. TV or internal screen switch.
One option is to just run video to both your video out and to the internal screen. The video signal will not be as good as it is split, but the other option would be to put your video signal through a switch. You'd need an IC to do this with HDMI since you'd have to switch all of the video outputs.
It's around $15 shipped. The store is currently under renovation though.
Hopefully this helps you, but you really need to read through all the material on the site. We're happy to help out beginners, but building a portable is not something that is spoonfed. It requires a lot of research and study if you want to be successful. Best of luck!
