1) - Can't help you, sorry
2) - most auto parts stores have a section for specialty items like these plastic panel clips.
3) - OEM speakers are 4 1/2" round. You can modify the brackets to take something larger if needed but it's a pain.
4) - OEM knobs are available from isuzuparts.com or there are usually some on Ebay. Hit the Facebook group and look for Dan Danlister. He has a business of parting out VX's.
5) - Dan Danlister on the VehiCROSS Facebook page.
6) - These can be rebuilt at most shops that do custom BMX suspensions. If you can't find someone local then there is a place in CO and one in CA that you can ship to.
Hope this is helpful. Welcome to the addiction!
Live, Love, Forgive and Never Give Up