1) I'll leave this for the BMW-F mod squad.
2) Any of the brand name products are good. Everyone has their opinion/favorite.Click here for a link to the major car care products by category or manufacturer.
Scroll down to see this info.
Note: I use/have used Armor All for over 20 years without a problem (old school), not as a cleaner but as a conditioner. I clean first with a gentle cleaning solution, apply Armor All and then polish/wipe it off real good after applying it. This will leave a nice sheen and remove that wet look that is greasy, slippery, causes glare, attracts dust and generally looks bad.
IMO, for long term, no effort protection of your dash, purchasing a dash cover is the simplest, most cost effective method of protecting it. Try Bav Auto
for further info. You'll clean your dash about 10 times less often and reach your goal of keeping your dash from cracking.
3) I use Black again. It seems to work well on trim that is good condition. It doesn't last that long though. I'll probably try something else when I finish using what I have. Forever Black seems to get very good reviews for trim that needs restoring. Check the link above for add'l products. .
4) Synthetic Oil is the way to go. Less friction, better lubrication.
5) or 4II Bav Auto, again :-)