Which size and material V-Wheels should I get for the Z-axis?

Hello friends! Hope you are having a beautiful day ;-)

I am going to do my best to keep my question simple and to the point:

- Currently working on building a mendel style printer
- Using 2040 profile anodized aluminum rails for the Z-axis
- And recently found out about mini v-wheels AND the extreme solid line of products.

Here are my questions:

1. For my z-axis carriages, can I use the smaller diameter mini v-wheels or are they unsuitable for this kind of application?
2. Price difference is minimal. Do extreme solid v-wheels (mini or not) have any benefits over black delrin ones for this kind of application?

If you don't mind bonus question:

I have been told that "3 points make a plane, therefore 3 wheels are enough for a carriage". I am not an expert in designing motion systems. Should I use 3 or 4 wheels to guide the carriages, what's your recommendation?​

Thank you all for your kind help